Chapter 3: Clove and Some Relatives

Chapter 3: Clover and Some Relatives

ALSIKE CLOVER¹¹
Trifolium hybridum L., family Leguminosae

Alsike clover has been an important summer legume in north central and Northeastern United States; however, it is being replaced by alfalfa. A small amount of seed is produced in the Pacific Northwest. Most of the seed that we use comes from Canada. In 1969, we imported 3,715,000 pounds, most of which was probably used in mixed pasture planting.
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¹¹ See "Clovers General, " p. 158.

Plant:
Alsike clover is a perennial but usually grows as a biennial, and in some situations it behaves as an annual. It is intermediate in size between white and red clover. Many smooth stems, bearing smooth trifoliate leaves, arise from its crown. The noncreeping stems may grow to a height of 5 feet but usually reach about 2 feet. They bear flower heads along their entire length, the youngest always toward the top. It is a good hay, pasture, and green manure crop, and like other legumes, it improves the soil and contributes to reduced soil erosion.

Inflorescence:
The flower head of alsike clover is made up of many florets and is similar to the more common white clover, although there may be four times as many heads per square yard as are normally found on white clover. The florets on some heads are pink, on others they are white, and on some they are both pink and white. This variation in flower color led to an earlier belief that alsike was a cross between red and white clover, hence the scientific name hybridum.

A floret will produce two to three seeds. Flower heads with 100 seeds indicate a good seed crop. The flowers are quite attractive to bees, especially honey bees, for the nectar and pollen. Pellett (1923) stated that some beekeepers estimated that alsike clover might produce 500 pounds of honey per acre in good seasons. This seems abnormally high but indicates the importance beekeepers attach to this crop as a source of honey. Holmes (1960) noted that boron favorably influenced nectar secretion in alsike clover, but apparently this information has not been used to increase seed production.

Pollination Requirements:
The florets are largely self-incompatible so they must receive pollen from another plant to produce seed (Pieters and Hollowell 1937). In Ohio, Dunham (1939) showed that three cultivars set only 0.4 to 5.5 seeds per head when selfed, 3.4 seeds per head when wind pollinated, and 120 to 125 seeds per head in a cage with bees. Open plots had 2.6 to 90.4 seeds per head. He calculated that the seed yielding capacity of a field with 1,000 heads per square yard, averaging 50 seeds per head, would be 350 pounds per acre, 90 seeds per head would produce 625 lb/acre and with 120 seeds per head the yield would be 825 lb/acre.

In Oregon, Scullen (1956*) reported 5.1 seeds per head where bees were excluded but 69.2 seeds per head where bees had access to them. (About 500 lb/acre, according to Dunham's (1939) method of calculation.) Oregon averages 300 to 415 lb/acre, but occasional phenomenal yields of 1,000 lb/acre are obtained. The overall United States average is about 140 lb/acre (Wheeler and Hill 1957*). Evidently, seed production in most areas could be significantly increased with adequate pollination.

Pollinators:
Few detailed studies have been made on the insect pollinators of alsike clover. Megee and Kelty (1932) concluded that the honey bee was an effective pollinator on alsike clover in Michigan. Dunham (1957) studied alsike clover seed setting for a number of years in an area of Ohio where intensive farming was practiced. He found that native bees set only 1.5 to 3 percent of the seeds. Valle (1960) reported that in Finland the honey bee was a much more important pollinator of alsike clover than bumble bees. According to Pankiw and Elliott (1959), the honey bee is the primary pollinator of alsike clover in western Canada. They found that fields with higher populations of pollinators matured earlier as well as produced more seed. Harrison et al. (1945) concluded that honey bees were essential to alsike clover in Michigan. Tucker et al. (1958) reported that honey bees comprised 93 to 99 percent of the pollinating insects on alsike clover in Minnesota. Smith (1960) stated that honey bees represent 83 percent of the total pollinator population on alsike fields in southern Ontario.

Pankiw and Elliott (1959) stated that honey bees are excellent pollinators of alsike clover and that they visited the florets at the rate of 18.7 per minute, as compared to 20.0 per minute for leafcutter bees, and 28.6 per minute for bumble bees. Fischer (1954) reported that honey bees will leave alsike for sweetclover. Wahlin (1962) observed that when widespread cultivation of oil plants occurred in the red and alsike clover seed growing area of Sweden, the bees visited these crops, which resulted in a reduced clover seed harvest.

Holdawav et al. (1957) in three observations over 2 years obtained yields of 15, 20, and 20 pounds of seed per acre without insect pollination; 102, 207, and 368 lb/acre with insect pollination, no harmful insect control and no fertilizer added; and 685, 691, and 808 pounds of seed per acre with pollination, harmful insect control, and the addition of phosphorus and potash fertilizers. They recommended at least two colonies per acre, the colonies placed at the edge of the field.

Studies have established that the honey bee is the primary insect pollinator of alsike clover and its activity accounts for the bulk of the seed produced. Evidently, seed production of this crop can be significantly increased over current commercial averages if honey bees are present in adequate numbers.

Pollination Recommendations and Practices:
Pankiw and Elliott (1959) recommended one colony of honey bees per acre of alsike clover for fields of 50 acres or more but up to three colonies per acre for smaller fields. They obtained about 375 pounds of seed per acre with a bee population of about three-quarters of a bee per square yard. Smith (1960) recommended two to three colonies per acre with the colonies placed in or close to the field. Holdaway et al. (1957) recommended at least two colonies per acre. Tucker et al. (1958) concluded that seed yields were increased about 260 lb/acre for each colony per acre. They calculated that one bee per 3 yd2 set 175 pounds of seed per acre, but one bee per square yard set 800 pounds of seed per acre. The number of colonies per acre necessary to provide the one bee per square yard was not indicated.

Dunham (1938) thought that the number of colonies necessary to provide maximum pollination of alsike might be so great it would make the renting of bees prohibitive. No study has been made to determine this factor. The data indicate, however, that the alsike seed grower can afford to and should obtain several colonies per acre at current colony rental prices (see "Pollination Agreements and Services").

LITERATURE CITED:
DUNHAM, W. E.
1938. INSECT P0LLINATION OF ALSIKE CL0VER. Gleanings Bee Cult. 66: 425.

______ 1939. THE IMPORTANCE OF HONEYBEES IN ALSIKE SEED PRODUCTION. Gleanings Bee Cult. 67: 356-358, 394.

DUNHAM, W. E.
1957. GREATER BEE CONCENTRATION IS NEEDED FOR ADEQUATE POLLINATION OF CLOVER FIELDS. Gleanings Bee Cult. 85: 218-219.

FISCHER, R. L.
1954. HONEYBEES AID PRODUCTION OF ALSIKE CLOVER SEED. Minn. Farm and Home Sci. 11(3): 7-9.

HARRISON, C. M., KELTY, R. H., and BLUMER, C.
1945. HONEYBEES AND LEGUME SEED PRODUCTION. Mich. Agr. Expt. Sta. Quart. Bul. 28(2): 1 - 5.

HOLDAWAY, F. G., BURSON, P. M., PETERSON, A. G., and others.
1957. BETTER LEGUME SEED PRODUCTION. Minn. Farm and Home Sci. 14(3): 11-13.

HOLMES, F. O.
1960. BORON DEFICIENCY AS A PROBABLE CAUSE OF THE FAILURE OF BEES TO VISIT CERTAIN FLOWERS. Amer. Bee Jour. IOO: 102 - 103.

MEGEE, C. R., and KELTY R. H.
1932. THE INFLUENCE OF BEES UPON CL0VER AND ALFALFA SEED PRODUCTION. Mich. Agr. Expt. Sta. Quart. Bul. 14(4): 271-277.

PANKIW, P., and ELLI0TT, C. R.
1959. ALSIKE CL0VER P0LLINATION BY HONEY BEES IN THE PEACE RIVER REGION. Canad. Jour. Plant Sci. 39(4): 505-511.

PELLETT F. C.
1923. AMERICAN HONEY PLANTS. 392 pp. American Bee Journal, Hamilton, III.

PIETERS, A. J., and HOLLOWELL, E. A.
1937. CL0VER IMPROVEMENT. U.S. Dept. Agr. Yearbook 1937: 1190-1214.

SMITH M. V.
1960. LEGUME P0LLINATION IN ONTARI0. Ontario Dept. Agr. Pub. 139, 7 pp., Toronto.

TUCKER, K. W., FURGALA, B., and KIECKHEFER, R. W.
1958. HONEY BEES INCREASE ALSIKE CL0VER SEED YIELDS. Minn. Farm and Home Sci. 15(2): 3.

VALLE, O.
1960. [POSSIBILITIES OF ALSIKE CLOVER SEED PRODUCTION IN FINLAND. Maatalous ja Koetoim. 14: 118-127. [In Finnish, English summary.] AA-395/62.

WAHLIN, B.
1962. THE UTILIZATION OF HONEY BEES IN SEED PRODUCTION. In 1st Internatl. Symposium on Pollination Proc., Copenhagen, Aug. 1960, Commun. 7, Swedish Seed Growers' Assoc., pp.95-97.

ARROWLEAF CLOVER¹²Trifolium vesiculosum Savi, family Leguminosae
Arrowleaf clover is a winter annual clover adapted to well-drained soils in most areas of coastal Georgia to Mississippi where it is grown on a limited scale.

Plant:
Arrowleaf clover may grow 20 to 28 inches tall with stems to 40 inches long. Although it is later in maturity and produces less during the winter and early spring, it exceeds crimson clover in annual forage yield. There are several cultivars including 'Amclo' (Beaty et al. 1963), 'Yuchi' (Hoveland 1967), and 'Meechee' (Knight et al. 1969). The 'Yuchi' cv. is productive for 2 months longer in the spring than crimson clover, tolerant to drought, and resistant to the alfalfa weevil and the cloverhead weevil (Hoveland et al. 1969). It is not adapted to alkaline soils.

Inflorescence:
The white flower head, which turns to pink and then purple, is conical, 2 inches or more long by 1 l/4 inches across, and consists of 50 to 170 florets. Each floret is capable of producing two to three seeds. The 'Yuchi' cv. flowers from May to July (Hoveland et al. 1969). Seed yields of 100 to 500 lb/acre have been reported.

Pollination Requirements:
Hoveland et al. (1969) stated that bees are essential for pollinating arrowleaf clover.

Pollinators:
Apparently, honey bees are good pollinators of arrowleaf clover, just as they are for many other clovers.

Pollination Recommendations:
According to Hoveland et al. (1969), one colony of honey bees is recommended per acre, but no data are given to support this recommendation.

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¹² See "Clovers, General," p. 158.

LITERATURE CITED:
BEATY, E. R., POWELL, J. D., and YOUNG, W. C.
1963. AMCLO ARROWLEAF CLOVER. Crop Sci. 5: 284.

HOVELAND, C. S.
1967. REGISTRATION OF YUCHI ARROWLEAF CL0VER. Crop Sci. 7: 80.

____ GARDEN, E. L., BUCHANAN, G. A., and others.
1969. YUCHT ARROWLEAF CLOVER. Ala. Agr. Expt. Sta. Bul. 396,27 pp.

KNIGHT, W. E., ALDRICH V. E., and BYRD, M.
1969. REGISTRATION OF MEECHEE ARROWLEAF CLOVER Crop Sci. 9: 393.

BALL CLOVER¹⁴Trifolium nigrescens Viv., family Leguminosae
Plant:
Ball clover is a reseeding, annual, hollow-stem, creeping legume that does not root at the nodes. It reaches 18 to 36 inches high, and resembles Persian clover. It is grown to a minor degree in the Gulf Coast States and has been grown as far north as Maryland and as far inland as Missouri.
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¹⁴ See "Clovers, General," p. 158.

Inflorescence:
The flowers are smaller than those of white clover, highly fragrant, and highly attractive to bees. The flower heads have an average of 38 florets. Ball clover blooms over a period of 7 to 8 weeks and has a high density of blooms (840/yd2 ). Perkins (1961) counted 2,285 full to partly open florets per square yard. He also
(1960) recorded 840 mature flower heads per square yard, compared with 315 white clover and 300 crimson clover heads.

Ball clover is an excellent honey plant, and bees show a strong preference for it over other true clovers. Other bees are also attracted to it.

Pollination Requirements:
Weaver and Weihing (1960) obtained more than 100 times as much seed from caged plots with bees as from plots caged to exclude bees. They concluded that pollinating insects are necessary for seed production. Perkins (1961) stated that Òball clover is self-fertile but, like crimson, pollinators increase seed yields.Ó His observations indicated that because of its attractiveness to honey bees there should be little trouble in getting bees to visit the flowers. The desired visits per unit of flowers for maximum seed production are unknown.

Pollination Recomendations and Practices:
There are no recommendations for the use of pollinating insects on ball clover, nor is there an indication that growers take steps to utilize such insect activity to obtain maximum seed production.

LITERATURE CITED:
PERKINS, G.
1960. BALL CLOVER, TRIFOLIUM NIGRESCENS. Gleanings Bee Cult. 88: 684-685, 701.

______ 1961a. MORE ABOUT BALL CLOVER. Gleanings Bee Cult. 89: 92, 123.

______ 1961b. BALL CLOVER - LOOKS PROMISING FOR A SOUTHERN BEE PASTURE Gleanings Bee Cult. 89: 614-615.

WEAVER, N., and WEIHING R. M
1960. POLLINATION OF SEVERAL CLOVERS BY HONEYBEES. Agron. Jour. 52: 183-185.

BERSEEM CLOVER¹⁶Trifolium alexandrinum L., family Leguminosae
Berseem, or Egyptian clover, is a little-known legume in the United States. It is grown to a small extent in southern California, Arizona, Texas, and in other States near the Gulf of Mexico where freezing rarely occurs (Wheeler and Hill 1957*). Temperatures below 25¡ F are frequently fatal to berseem plants (Bashaw and Riewe 1955).
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¹⁶See "Clovers, General," p. 158

Plant:
Berseem is an erect, 18- to 36-inch, nonreseeding, cool-season, hollow-stem, annual clover, recognizable by its typical cloverlike appearance (Kretschmer 1964). It is a heavy forage producer and grows extremely fast in the mild winter areas. It is grown primarily for its succulent, high-quality forage, which cattle prefer over alfalfa. Hassanein (1953) considered berseem to be the most important forage crop in Egypt. It grows from October to May but produces forage principally from December to March. Seed yields vary from 150 to 500 lb/acre (Wheeler and Hill 1957*).

Inflorescence:
The round to oblong yellowish heads, similar in size and structure to white clover heads, appear shortly after the first of the year. The florets (fig. 50) form one seed each. Berseem is highly attractive to bees, which visit it avidly for nectar and pollen. It sets seed abundantly, more than 70 per head, if pollinating insects are present (Narayanan et al. 1961). Unlike alfalfa, the most vigorous berseem plants set the most seed (Kennedy and Mackie 1925).

Pollination Requirements:
For such a minor crop, the pollination of berseem is quite well established. Chowdhury et al. (1966) stated that it is self-compatible, but tripping is essential for seed set. They stated that wind was an important pollinating agent but presented no data to support this statement. Shamel (1905) reported that bees are absolutely necessary for pollination. This has been verified with caged and open plots by Hassanein (1953), Latif (1956), and Narayanan et al. (1961). The reports leave little doubt that insect pollination is absolutely necessary for profitable seed production. Narayanan et al. (1961) obtained from 19.58 to 70.54 seeds per head of open pollinated berseem plants but only 0.27 to 0.64 seed per head where insects were excluded by 16-mesh wire gauze cages.

Pollinators:
Honey bees are the primary pollinators of berseem. They collect both nectar and pollen (Narayanan et al. 1961).

Pollination Recomendations and Practices:
There are no recommendations on the use of insect pollinators on berseem. Considering its flowering characteristics, the absolute necessity of bees in its pollination, and the time of year it blooms, the equivalent of two to four bees per square yard should be sufficient to set a maximum crop of seed.

LITERATURE CITED:
BASHAW, E. C., and RIEWE, M.
1955. EFFECT OF PERIODIC LOW TEMPERATURE ON BERSEEM CLOVER. Tex. Agr. Expt. Sta. Prog. Rpt. 1818, 3 pp.

CHOWDHURY, J. B., MEHTA, R. K., and JOSHI, A. B.
1966. POLLINATION IN BERSEEM. Indian Jour. Genet. and Plant Breed. 26: 118-120.

HASSANEIN, M. H.
1953. STUDIES ON THE EFFECT OF POLLINATING INSECTS, ESPECIALLY THE HONEYBEE, ON THE SEED YIELD OF CLOVER IN EGYPT. Soc. Fouad ler d'Ent. Bul. 37: 337-344. AA-124/54.

KENNEDY, P. A., and MACKIE, W. W.
1925. BERSEEM OR EGYPTIAN CLOVER, TRIFOLIUM ALEXANDRINUM L. Calif. Agr. Expt. Sta. Bul. 389, 32 pp.

KRETSCHMER, A. E., JR.
1964. BERSEEM CLOVER - A NEW WINTER ANNUAL FOR FLORIDA. Fla. Agr. Expt. Sta. Cir. S-163, 16 pp.

LATIF, A.
1956. ROLE OF APIS INDICA F. IN THE POLLINATION OF EGYPTIAN CLOVER (TRIFOLIUM ALEXANDRINUM LINN.). Pakistan Jour. Sci. Res. 8(1): 48-50. AA-32/59.

NARAYANAN, E. S., SHARMA, P. L., and PHADKE, K. G.
1961. STUDIES ON REQUIREMENTS OF VARIOUS CROPS FOR INSECT POLLINATION - INSECT POLLINATORS OF BERSEEM - EGYPTIAN CLOVER (TRIFOLIUM ALEXANDRINUM) WITH PARTICULAR REFERENCE TO HONEY BEES AND THEIR ROLE IN SEED SETTING. Indian Bee Jour. 23(4/6): 23-30.

SHAMEL, A. D.
1905. RELATION OF BEES TO FERTILIZATION OF CLOVERS. U.S. Dept. Agr. Yearbook 1905: 385-386.

BLACK MEDIC OR YELLOW TREFOIL
Medicago lupulina L., family Leguminosae
Black medic or yellow trefoil, a near relative of alfalfa and burclover, is widely distributed in the South but is seldom abundant in one location.

Plant:
The annual or biennial plant that reseeds readily has slender, finely pubescent, procumbent stems from a few inches to two feet long, with hairy leaflets l/4 to 3/4 inch long. It is an introduced yellow-flowered European legume that has escaped in waste places throughout the country (Graham 1941*, Martin and Leonard 1949*).

Inflorescence:
Black medic bears small, bright-yellow flowers in dense heads, l/2 inch or less in length. The mechanism of the small (2 mm) flower is similar to that of alfalfa. An insect visit causes the sexual column to trip, but, unlike the alfalfa sexual column, it does not return to its original position in the keel when the pressure is removed.

Pollination Requirements:
Bohart (1960*) stated that black medic is self-fertile and self- pollinating and thus has no need for pollinating insects.

Knuth (1908*, p. 279 - 280) also stated that automatic self- pollination takes place readily, but that it is far less productive than cross-pollination. Apparently, like ball and crimson clover, black medic will set seed in selfed flowers, but more seeds will set if crossing occurs. Todd (1957*) listed black medic as a crop whose seed production is increased by bees.

Hartwig (1953) stated that florets were more likely to be fertilized if visited by insects.

Pollinators:
Honey bees are the chief visitors to black medic flowers. They visit a few flowers on an inflorescence then move to other inflorescences, thereby increasing possible crossing. Many other bees are of some value as pollinators.

Pollination Recommendations and Practices:
No recommendations have been made for use of insect pollinators on black medic; however, the meager data available indicate that many bees are needed for maximum seed production.

LITERATURE CITED:
HARTWIG, H. B.
1953. LEGUME CULTURE AND PICTURE IDENTIFICATION. 42 pp. M. S. Hartwig, Ithaca, N.Y.

CIDER MILKVETCH
Astragalus cider L., family Leguminosae
Cider milkvetch offers possibilities as a good pasture crop in the irrigated and dryland areas in the Great Plains and Western States. Apparently, it is not grown commercially, although Hafenrichter et al. (1968) considered it superior to alfalfa. Townsend (1970) pointed out that there is a scanty information on this crop.

Plant:
Cider milkvetch is a perennial legume, 2 to 3 feet tall, that spreads by rhizomes. In growth characteristic, it varies from decumbent to prostrate. Like most of the members of Astragalus, it is well adapted to arid conditions (Bleak 1969). Although little work has been done on Astragalus spp., it is known that some species are useful honey plants, whereas other species are poisonous to bees and livestock (McKee and Pieters 1 937).

Inflorescence:
The typical papilionaceous flowers of yellow or purple are in axillary racemes or heads with many ovules. At Fort Collins, Colo., flowering occurs during June and July (Townsend 1970).

Pollination Requirements:
Townsend (1971a) reported good seed-set on open-pollinated cicer milkvetch plants at Fort Collins but obtained no seed from 1,400 non- manipulated florets on plants in a growth chamber (1971b). Those that were manipulated set 5.29 seeds per raceme, whereas the open-pollinated racemes set 100 to 300 seeds each. In personal communication (1971), Townsend stated that in his opinion little seed would be set on A. cicer in the field without insect pollinators.

The Gifu (Japan) Agricultural Experiment Station (1954) conducted a test on the value of honey bees in the pollination and seed setting of a species referred to as A. sinensis. Seed production in cages where bees were excluded was only about 70 lb/acre; in cages with honey bees it was almost doubled, 130 lb/acre, and in open plots, 980 lb/acre. The reason for the great difference between caged and open plots was likely due to the cage effect. The relation between the pollination requirements of A. cicer and A. sinensis is not clear.

If A. cicer develops into a crop of importance, its need for and importance of insect pollination should be established.

Pollinators:
Honey bees appear to be satisfactory pollinators of A. sinensis. Their value on A. cicer is unknown but should be determined.

Pollination Recommendations and Practices:
None.

LITERATURE CITED:
BLEAK, A. T.
1969. GROWTH AND YIELD OF LEGUMES IN MIXTURES WITH GRASSES ON A MOUNTAIN RANGE. Jour. Range Mangt. 21: 259 - 261.

GIFU AGRICULTURAL EXPERIMENT STATION [JAPAN].
1954. [HONEYBEES AND THE SEED PRODUCTION OF CHINESE MILK VETCH.] Gifu Agr. Expt. Sta., 11 pp. [In Japanese.] AA-66/59.

HAFENRICHTER, A. L., SCHWENDIMAN, J. L., HARRIS, H. L., and others.
1968. GRASSES AND LEGUMES FOR S0IL CONSERVATION IN THE PACIFIC NORTHWEST AND GREAT BASIN STATES. U.S. Dept. Agr. Agr. Handb. 339, 69 pp.

McKEE, R., and PIETERS, A. J.
1937. MISCELLANEOUS FORAGE AND COVERCROP LEGUMES. U.S. Dept. Agr. Yearbook 1937: 999 - 1031. TOWNSEND. C. E. 1970. PHENOTYPIC DIVERSITY FOR AGRONOMIC CHARACTERS IN ASTRAGALUS CICER L. Crop Sci. 10: 691-692.

______ 1971a. ASSOCIATION AMONG CHARACTERS RELATED TO SEED PRODUCTION IN ASTRAGALUS CICER L. Crop Sci. 11: 307-308.

______ 1971b. SELF-COMPATIBILITY STUDIES WITH ASTRAGALUS CICER L. Crop Sci. 11: 769 - 770.

CLOVERS, GENERAL
Family Leguminosae
Numerous species of plants in different genera of the family Leguminosae are called clover. They have certain characteristics in common. The leaf is normally composed of three leaflets. The papilionaceous (butterfly-like) or pealike floret of the flower head consists of a large dorsal standard petal, two lateral wing petals, and two lower keel petals. It usually has 10 stamens, one of which is free and the other nine united, that form a tube enclosing the long ovary. The flower trips exposing the stigma, which returns to its original position after pressure on the petals is removed. The plants have the ability to take nitrogen from the air and, by Rhizobium fixation, store it within nodules on the roots. This contributes to the value of the plant to the soil. The plants provide excellent forage for livestock, and they help in erosion control. Many of the species are good sources of honey and pollen for bees.

The United States Government considers legume crops so important that in 1946, when seed stocks were in short supply, Congress appropriated funds to encourage the harvesting of seeds of these crops (Johnson and Loomer 1948).

The hay crop from clover and clover mixtures in 1969 was harvested from slightly more than 13 million acres.

There are about 250 species of Trifolium, the True Clovers, but only four make up the bulk of the acreage. They are alsike clover (T. hybridum L.), crimson clover (T. incarnatum L.), red clover (T. pratense L.), and white clover (T. repens L.).

There are about 20 species of Melilotus, the sweetclovers, but only three species make up the bulk of the acreage. They are biennial yellow sweetclover (M. officinalis (L.) Lam.), biennial white sweetclover (M. alba Desr.), the annual white subspecies (M. a. var. annua Coe), and yellow annual sourclover or sour sweetclover (M. indica (L.) All.).

There are about 65 species of Medicago, some species of which are referred to as clover, for example, the burclovers, two species of which are important. They are toothed burclover (M. hispida Gaertn.) and spotted burclover (M. arabica Huds.). Alfalfa (M. sativa L.) is the most important species.

There are 16 species of Alysicarpus, or Alyce clover, which is not a True Clover, but none are of great economic importance.

There are about 70 species of Lespedeza or bush clover, several of which are of economic importance.

Weaver and Weihing (1960) concluded, with limited cage tests, that pollinating insects were essential for adequate seed production of the experimental species Trifolium isthmocarpum Brot., T. michelianum Savi, T. pallidum Waldst. & Kit., and T. xerocephalum Fenzl.

A memorandum to USDA cooperators, from R. C. Leffel (USDA, Clover Investigations, 1971), listed the following cultivars of clover available for agronomic evaluation: Cluster clover (T. glomeratum L.), Kura clover (T. ambiguum Bieb.), Lappa clover (T. Iappaceum L.), Large Hop clover (T. campestre Schreb.), Small Hop clover (T. dubium Sibth.), and Striate clover (T. striatum L.). Leffel mentioned that other species may also be present in agronomists' test plots, but none are currently grown commercially. Their pollination requirements are unknown but should definitely be evaluated by the agronomists along with their other characteristics, if release of the species for commercial production appears likely.

The important species of these different genera that are known to be dependent upon or benefited by insect pollination are discussed as separate crops herein.

LITERATURE CITED:
JOHNSON, N. W., and LOOMER,C.W.
1948. THE HELP THE GOVERNMENT OFFERS. U.S. Dept. Agr. Yearbook 1948: 34-44.

WEAVER, N., and WEIHING,R.M.
1960. POLLINATION OF SEVERAL CLOVERS BY HONEYBEES. Agron. jour. 52: 183-185.

CRIMSON CLOVER²⁶
Trifolium incarnatum L., family Leguminosae
Crimson clover is an important and colorful winter annual legume in the South and is grown to some extent on the Pacific coast, where winters are mild. It is also grown in some Northern States as a summer annual. Alabama, Georgia, and Tennessee, in that order, were the leading producers of crimson clover seed, but most of it is now produced in Oregon. More than 2.5 million pounds were produced in 1970.

Compared to other clovers, crimson clover is a heavy producer of seed. Yields of 300 to 600 pounds per acre are common, and yields of 1,000 to 1,200 pounds have been obtained (Wheeler and Hill 1957*).
__________
²⁶ See "Clovers, General."

Plant:
Crimson clover grows erect to about 2 feet tall, and is easily recognized by its crimson flowers that are about 2 inches long by 1 inch wide. It resembles red clover, but its leaves have a more rounded tip, and both the stems and leaves have more hair on them than does red clover. It is usually sown and develops a crown of growth in the fall. In the spring, fresh stems form, then terminate in the long, pointed flower head. Flowering in the South occurs in April. The seeds develop, then with the coming of summer weather, the plant dies.

The plant is widely used as forage, pasture, green manure, and an erosion control plant. It has the advantage of producing large quantities of seed that can be, easily harvested and planted without the use of expensive equipment (Hollowell 1938).

Inflorescence:
The 65 to 125 crimson florets that make up the colorful crimson clover head are typically Trifolium and roughly 5/8 inch long by 1/8 inch wide. Weaver and Ford (1953) recorded 96 florets per flower head and estimated roughly 2 million flower heads per acre. Amos (1950) estimated 200 million florets per acre.

Knight and Green (1957) stated that although honey bees are attracted to crimson clover they have difficulty in forcing their mouth parts into the floret. The bee trips the floret whether nectar or pollen is collected. Knight (1969) found that an apetalous male-sterile selection was unattractive to bees.

Girardeau (1958), Lovell (1926), and Pellett (1947*) rated crimson clover high as a honey plant. The quality of honey produced is excellent. Girardeau (1954) stated that when bees forage on crimson clover they do not crowd their broodnest with honey. Girardeau (l 958) observed that bees collected nectar from crimson clover primarily in the mornings and pollen in the afternoons. This is exceptional because most plants that attract bees for pollen do so in the forenoons. The pollen is collected in large amounts and this, also, is unusual for leguminous plants. Girardeau (1958) also noticed that cells filled with crimson clover pollen were scattered throughout the honey storage area instead of being concentrated around the broodnest, and that colonies foraging on this crop swarmed excessively. No reasons were determined for these behaviorial differences.

Pollination Requirements:
The crimson clover floret is self-fertile but is not self-tripping (USDA 1967), therefore pollinating insects are required for profitable seed production (Pieters and Hollowell 1934). The flower is easily tripped. After tripping and release of pressure on the keel petal by the bee, the stamina! column returns to its original position. No data have been obtained on the value of repeated bee visits to a floret. If the floret is pollinated, it withers within a day's time; but if not pollinated, it will remain fresh-looking for about 2 weeks. This characteristic contributes to the flower-garden appearance of a poorly pollinated field and the dull appearance of a well-pollinated field (Knight and Green 1957).

Pollinators:
There seems little doubt that honey bees are the primary pollinators of crimson clover. Knight and Green (1957) stated that wild bees, such as bumble bees, do not pollinate much crimson clover. They accredited wind and rain with 13 to 20 percent of the pollination in the open. Scullen (1956*) observed that the flowers were attractive to bumble bees and some species of wild bees in Oregon, but in general he indicated that they alone were insufficient. Girardeau (1958) found that because of the early flowering of crimson clover in the spring in Georgia, few bees other than honey bees were active in the field. Beckham and Girardeau (1954) reported that about 2 percent of the bees in the field were bumble bees, the rest honey bees.

Weaver and Ford (1953) stated that virtually all of the pollination seemed to have been performed by honey bees. Blake (1955) reported that pods containing seeds and seed yields were always higher near apiaries. Hollowell (1947) stated that bees were effective as tripping agents and in the transfer of pollen from flower to flower, with a consequent increase in the number of seeds per head. Wheeler and Hill (1957*) stated that placing colonies of bees near fields has increased yields in some cases up to 1,000 to 1,200 lb/acre.

The effect of honey bees as pollinators has also been established with cage tests. Amos (1950,1951) obtained only 2.64 g of seed from 50 crimson clover heads caged under 2-, 4-, or 16-mesh per inch screen to exclude various types of bees, but harvested 6.36 g per 50 heads exposed to one colony of honey bees per acre. Scullen (1956*) obtained five seeds per head excluded from bees, but 69 seeds per head available to bees. Beckham and Girardeau (1954) harvested 130 lb/acre from caged plots but 491 lb/acre from open fields supplied with one colony per acre. Blake (1958) obtained 1,019 lb/acre with three colonies per acre and best agronomic practices, a gain of more than 800 pounds over production where bees were excluded. Killinger and Haynie (1952) harvested only 3 lb/acre in cages where bees were excluded, 64 lb/acre from cages with bees, and 105 lb/acre from open plots. Weaver and Ford (1953) harvested 59 lb/acre from cages where bees were excluded, 233 lb/acre from bee cages, and 297 lb/acre in open plots. (Eight colonies of bees were one-half mile from the 4-acre experimental plot.)

Johnson and Nettles (1953) obtained 37 pounds of seed per acre in caged plots but 375 lb/acre in the open field where there were 2.5 colonies of honey bees per acre. Vansell²⁷ reported that he obtained 5.08 seeds per head on caged crimson clover plots in Oregon and 69.2 seeds per head in the open field. He stated that a 144-acre field in Hanford, Calif., supplied with three colonies of honey bees per acre produced 1,100 pounds of seed per acre.
__________
²⁷ VANSELL, G. H. POLLINATION STUDIES. U.S. Dept. Agr., Pacific States Bee Cult. Field Lab., Davis, Calif., First Quart. Rpt. of Prog., p. 17. 1952. [Processed.]

Pollination Recommendations and Practices:
The need for honey bees as pollinators in the production of crimson clover seed is firmly established. The number of bees required is less firm. In Texas, Weaver and Ford (1953) calculated that one colony of honey bees per acre should be sufficient to saturate any field of crimson clover, providing there was not too much competition from other sources of pollen and nectar. Pedersen et al. (1961) and Girardeau (1958) also recommended one colony per acre. Killinger and Haynie (1952) recommended one colony per acre, but they stated that some increase in seed production was obtained with up to five colonies per acre. Blake (1958) recommended two colonies per acre in Alabama, and, when three colonies per acre were used, the exceptionally good yield of 1,019 lb/acre was obtained. Hollowell and Knight (1962) recommended the placement of the colonies of honey bees in or adjacent to the field, and they stated that, with good clover stands and good pollination, yields of 1,000 to 1,200 pounds of seed per acre could be obtained.

Weaver and Ford (1953) stated, "The clover itself gives a reliable indication of whether there are adequate numbers of pollinating insects in the field. When the blossoms are not pollinated they remain open for about 2 weeks before they wither. Blossoms which are pollinated, however, wither within a day. In the cages from which all insects are excluded, the blossoms open in successive whorls from the bottom, and remain open until the entire flower head is a solid mass of beautiful open florets. When adequate pollinating insects are present, however, there is a narrow whorl of open blossoms with buds above and withered flowers below. A field with some pollinating insects, but in inadequate numbers, has an "intermediate, or rather spotted appearance."

Knight and Green (1957) stated that close proximity of a field to honey bee colonies does not guarantee good pollination because of possible competition by other plants. They offered a much better method of estimating pollinator populations - bee visitors on the clover flowers. They believed that from two to three bees per 100 flower heads was an adequate population for good pollination. The counts should be made between 10 a.m. and 3 p.m., on a warm day with the clover in full bloom. They warned that "Since the peak of blooming and pollination is so short, it is often too late to get more bees when their need is discovered and the counts may be of value only for the next year." The grower might be wise to assure himself of a higher bee population in the field before peak bloom to insure adequate pollination at that time. By doing this, his field would never become a flower garden but would yield the maximum crop of seed.

LITERATURE CITED:
AMOS, J. M
1950. PRODUCE MORE CRIMSON CLOVER SEED WITH HONEYBEES. Tenn. Mkt. Bu1.22(11): 6 - 7.

____ 1951. THE EFFECT OF HONEYBEES ON THE POLLINATION OF CRIMSON CLOVER. Amer. Bee Jour.91: 331 - 333. 200

BECKHAM, C. M., and GIRARDEAU, J. H., JR.
1954. A STUDY OF HONEYBEES AS POLLINATORS OF CRIMSON CLOVER. Assoc. South. Agr. Workers Proc. 51st Ann. Conv., p. 95.

BLAKE, G. H.
1955. CRIMSON CLOVER POLLINATION BY HONEY BEES. Assoc. South. Agr. Workers Proc. 52d Ann. Conv., p. 102.

____ 1958. THE INFLUENCE OF HONEY BEES ON THE PRODUCTION OF CRIMSON CLOVER SEED. Jour. Econ. Ent. 51: 523 - 527.

GIRARDEAU, J. H., JR.
1954. RESEEDING CRIMSON CLOVER - AS A MAJOR HONEY PLANT IN SOUTH GEORGIA. (Prelim. Rpt.) Ga. Agr. Expt. Sta. Mimeo Ser. n.s. 1: 1-7.

____ 1958. THE MUTUAL VALUE OF CRIMSON CLOVER PLANTINGS AND HONEY BEES FOR SEED AND HONEY PRODUCTION IN SOUTH GEORGIA. Ga. Agr. Expt. Sta. Mimeo Ser. n.s. 63: 1-23.

HOLLOWELL, E. A.
1938. CRIMSON CLOVER. U.S. Dept. Agr. Leaflet 160, 8 pp.

____ 1947. CRIMSON CLOVER. U.S. Dept. Agr. Leaflet 160, 8 pp.

____ and KNIGHT, W. E. 1962. CRIMSON CLOVER. In Hughes, H. D., Heath, M. E., and Metcalfe, D. S., Forages - The Science of Grassland Agriculture, ed. 2., pp. 180 - 186. The lowa State College Press, Ames.

JOHNSON, W. C., and NETTLES, W. C.
1953. POLLINATION OF CRIMSON CLOVER: 1952 DEMONSTRATION RESULTS. S.C. Ext. Serv., Misc. Publ. (Unnumbered), 6 pp.

KILLINGER, G. B. and HAYNIE, J. D.
1952. HONEYBEES AND OTHER FACTORS IN FLORIDAÕS LEGUME PROGRAM. Fla. Agr. Expt. Sta. Bul. 497, 14 pp.

KNIGHT, W. E.
1969. INHERITANCE OF AN APETALOUS, MALE-STERILE CHARACTER IN CRIMSON CLOVER. Crop Sci. 9: 94.

____ and GREEN, H. B. 1957. BEES NEEDED FOR POLLINATION OF CRIMSON CLOVER. Miss. Farm Res. 20: 7.

LOVELL, J. H.
1926. HONEY PLANTS OF NORTH AMERICA 408 pp. A. I. Root Co., Medina, Ohio.

PEDERSEN, M. W., JONES, L. G., and ROGERS, T. H.
1961. PRODUCING SEEDS OF THE LEGUMES. U.S. Dept. Agr. Yearbook 1961: 171-181.

PIETERS, A. J., and HOLLOWELL, E. A.
1937. CLOVER IMPROVEMENT. U.S. Dept. Agr. Yearbook 1937: 1190-1214.

UNITED STATES DEPARTMENT OF AGRICULTURE.
1967. GROWING CRIMSON CLOVER. U.S. Dept. Agr. Leaflet 482, 8 pp.

WEAVER, N., and FORD, R. N.
1953. POLLINATION OF CRIMSON CLOVER BY HONEYBEES Tex. Agr. Expt. Sta. Prog. Rpt. 1557, 4 pp.

CROWNVETCH
Coronilla varia L., family Leguminosae
Plant:
Crownvetch is a spreading, long-lived, winter-hardy, drought- tolerant, herbaceous legume with angular stems that grow to a height of 2 to 3 feet during the blooming period, after which the plant forms a dense mat about a foot deep. It will grow at fertility levels so low that few other plants will normally survive. Its principal use is for erosion control, soil building, and ground cover (Hawk 1955, Musser et al. 1954, Richardson and Diseker 1963, and Richardson et al. 1963). It is especially valuable for holding banks along highways. The stand improves with age and gradually chokes out other weeds. It is also used for its ornamental value on steep banks and hillsides (Grau 1962). The plant can be established from seeds or crowns (Wheeler and Hill 1957*).

Inflorescence:
Crownvetch produces attractive rose, white, or pinkish-white flowers from June to September. The inflorescence is a contracted raceme, and its flowers are a source of both nectar and pollen, which bees gather. The nectar is not secreted in the usual place but on the outside of the fleshy calyx, where it is sought out by bees (Muller 1883*). They alight upon the petals in the normal manner and probe with their proboscis between the bases of the petals to the outside of the flower for the nectar on the calyx (Knuth 1908*, p. 313, and Muller 1883*). Anderson (1958) stated that the honey bee has to learn how to trip crownvetch blossoms to obtain pollen, the primary attractiveness of the flowers, and, incidentally, to pollinate the blossoms.

The bee straddles the lower section of the flower with its head facing the center of the blossom; then with its two rear legs, the bee pushes the two sides of the blossom outward. This pressure causes the cup of the flower to shorten and the anthers and stigma to snap out where the pollen is available to the bee, and the stigma is exposed to pollination. Anderson also stated (personal correspondence, 1970) that bees have been known to starve on large acreages of crownvetch located in wooded areas of Pennsylvania.

Coronilla, meaning "little crown," is derived from the 202 characteristic crownlike shape of the cluster of blossoms. The specific name, varia, refers to variations in flower color as well as growth habits (Ruffner and Hall 1963).

Pollination Requirements:
Knuth (1908*, p. 313) indicated that crownvetch might not be self- pollinating. However, Todd (1957*) listed it as largely self-pollinated. Grace and Grau (1952) talked of the problem of low seed yields but did not mention pollination. Cope and Rawlings (1970) stated that it is almost completely cross-pollinated, and Al-Tikrity (1969) stated that it is entirely dependent upon insect pollination. Anderson (1958) showed that plants caged to exclude bees produced no seed, while similar plants caged with honey bees produced seed. He stated that a flower head consists of 12 fingerlets with 10 potential seeds in each fingerlet or 120 seeds per head. Eighty seeds per head is considered a good set. In the cage with bees, he obtained only 10 seeds per head, and in the open with few bees present he obtained 18 seeds. He attributed part of the low seed set in the cages to reduced light, but proved that crowavetch is self-sterile and that honey bees can and do pollinate it.

The following year, Anderson (1959) used plastic cages and more bees, and obtained 21.1 seeds per head in the cage and 24.6 seeds per head in the open despite the fact that weather was far less favorable for pollinator activity the second season. He also made repeated counts of pollinating insects in 8- by 50-foot plots, and recorded an average of 14 honey bees and 1.6 bumble bees. Other bees were negligible. Bumble bees visited 2.4 times as many blosoms per minute as did honey bees.

Henson (1963) compared seed production from bagged flowers tripped by hand, rolled, or untouched. The tripped flowers set twice as many seed as the rolled flowers and eight times as many as the untouched flowers. He showed that tripping increased seed production, but even this was low compared to the set obtained by Anderson (1959) when bees were used. Al-Tikrity (1969) reported 150 to 466 lb/acre.

Pollinators:
The observations by Anderson (1958,1959) showed that although crownvetch is not a good source of nectar for honey bees, they are its primary pollinators. Bumble bees visit 2.4 times as many blossoms per minute, but because of the scarcity of these bees they are far less effective and important than honey bees.

Pollination Recommendations and Practices:
Because it requires cross-pollination by insects, and because it is not overly attractive as a nectar source, probably a large number of colonies per acre would be required to provide a heavy bee population within the field. Anderson (1959), with 18 colonies of honey bees on 90 acres of crownvetch, obtained only 14 bees per 400 ft2Ñabout one-third bee per square yard and 24.6 seeds per blossom head (80 seeds per head is considered a good set). This would indicate that many more bees were needed, probably more than one per square yard, or more than one colony for each acre of crownvetch.

Al-Tikrity et al. (1970) suggested that three to four colonies per acre, arranged singly or in groups in rows 200 to 240 yards apart, would provide maximum pollination and result in high seed yields. Later, Al- Tikrity et al. (1972) suggested the moving of honey bees at the start of bloom, then additional colonies as blooming progressed. Sharp (1964) noted that when a good seed crop is being set, the field has a brownish cast. This could be an important factor in judging the effectiveness of the pollinating insects and possible needs for an increase in pollinator population.

LITERATURE CITED:
AL-TIKRITY, W. [S.]
1969. HONEY BEES (APIS MELLIFERA) AS CROWNVETCH (CORONILLA VARIA L.) POLLINATORS. 141 pp. M.S. Thesis, Pa. State Univ. Graduate School.

____ BENTON, A. W., CLARKE, W. W., JR., and HILLMANN, R. C.
1970. IMPROVING CROWNVETCH POLLINATION. Amer. Bee Jour. 110: 266 - 267.

____ BENTON, A. W., RISIUS, M. L., and CLARKE, W. W., JR.
1972. THE EFFECT OF LENGTH OF STAY OF A HONEYBEE COLONY IN A CROWNVETCH FIELD ON ITS FORAGING BEHAVIOR. Jour. Apic. Res. 11: 51 - 57.

ANDERSON, E. J.
1958. POLLINATION OF CROWN VETCH. Gleanings Bee Cult. 86: 281 - 283,318.

____ 1959. POLLINATION OF CROWN VETCH. Gleanings Bee Cult.87: 590 - 593.

COPE, W. A., and RAWLINGS, J. O.
1970. INHERITANCE OF FORAGE YIELD AND CERTAIN MORPHOLOGICAL AND FRUITING CHARACTERISTICS OF CROWN VETCH. Crop Sci. 10: 550-553.

GRACE, F. V., and GRAU, A. F.
1952. CROWNVETCHÑPROMISING NEW COVER CROP. Crops and SoiIS 4(9): 22-25.

GRAU, F. V.
1962. CROWNVETCH ``PENNGIFT', WHAT IT IS, WHAT IT DOES. Gard. Jour. 12(2): 65 - 66,72.

HAWK, V. B.
1955. CROWNVETCH, THE KUDZU OF THE NORTH. Iowa Soil DiSt. Watesheds Bul. 3(2): 6,16.

HENSON, P. R.
1963. CROWNVETCH - A SOIL CONSERVING LEGUME AND A POTENTIAL PASTURE AND HAY PLANT. U.S. Dept. Agr., Agr. Res. Serv. ARS 34-53, 9 pp.

MUSSER, H. B., HOTTENSTEIN, W. L., and STANFORD, J. P.
1954. PENNGIFT CROWNVETCH FOR SLOPE CONTROL ON PENNSYLVANIA HIGHWAYS. Pa. Agr. Expt. Sta. Bul. 576, 21 pp.

RICHARDSON, E. C., and DISEKER, E. G.
1963. CROWNVETCH STABILIZES PIEDMONT HIGHWAY BANKS. Crops and Soils 15: 25.

_____DISEKER, E. G., and HENDRICKSON, B. H.
1963. CROWNVETCH FOR HIGHWAY BANK STABILIZATION IN THE PIEDMONT UPLANDS OF GEORGIA. Agron. Jour. 55: 213.

RUFFNER, J. D., and HALL, J.G.
1963. CROWNVETCH IN WEST VIRGINIA. West Va. Agr. Expt. Sta. Bul. 487,19 pp.

SHARP. W.C.
1964. CROWNVETCH SEED PRODUCTION. U.S. Dept. Agr. Soil Conserv. Serv., pp. 1 - 5,58-60. Big Flats Plant Materials Center, Big Flats, N.Y.

LESPEDEZA
Lespedeza spp., family Leguminosae
Lespedeza is a crop of major importance in southeastern United States. Roughly 164,000 acres were grown for seed production in 1970, producing 36.8 million pounds of seed, valued at $5.2 million. Slightly more than 2 million tons of hay, valued at approximately $50 million, were produced in 1968, the last year the USDA Agricultural Statistics reported on the acreage of this crop.

Lespedeza is grown for hay and pasture, soil improvement, erosion control, seed, and its benefit to wildlife (game birds and deer).

Two types of lespedeza are grown - annual and perennial. The annuals, which are the most important (McKee l948),include 'Common' and 'Kobe' (L. striata (Thunb.) H. and A.) and 'Korean' (L. stipulacea Maxim.) (Elrod 1954). The most common perennial is 'Sericea' (L. cuneata (Dum.) G. Don) also known as shrub lespedeza (fig. 121). Three other perennial or shrub lespedezas, grown to a limited extent, are L. bicolor Turcz., L. intermedia (Wats.) Britt., and L. japonica Bailey.

[gfx] FIGURE 121. - Dense growth of 'Serica' lespedeza, which provides forage and cover for wildlife.

Plant:
The lespedezas are recognized by the small trifoliate leaves, l/4 to l/2 inch long, the individual flowers, and the one-seeded jointless pods. The annual lespedezas are often confused with hop clover although there are important differences. Hop clover seeds germinate in the fall, and the plants stay green throughout the winter and then die in early summer. Lespedeza seeds germinate in the spring, and the plants grow slowly until about the time hop clover dies. Also, the flowers differ in color (Essary 1921, Kinney and Kenney 1925). The plants are slightly spreading to erect, depending upon the thickness of the stem, and from a few inches to several feet tall, depending upon the species. The annuals grow to a height of 5 to 36 inches, depending upon soil moisture and fertility. The bush lespedezas reach 5 to 7 feet. At maturity, the leaves on Korean lespedeza turn forward so the branch tip resembles a cone (McKee 1940). In general, the growth habits of the annual lespedezas are like alfalfa (Pieters 1939a). 'Korean' lespedeza flowers are borne at the end of the branch, 'Common' flowers are borne all along the stem.

Lespedezas are drought-resistant, warm-weather plants. The hay contains less moisture when cut than alfalfa or clover, and can often be removed from the field after 1 day (Wheeler 1950). McKee and Pieters (1937) stated that only one species, L. striata, has been long known to agriculture.

Many cultivars of lespedeza exist. Probably the most extensively grown cvs. are: 'Kobe', 'Teen. 76', 'Harbin', 'Rowan', 'Summit', and 'Iowa Six' (Henson and Cope 1969). Seed production is limited to the southern part of the lespedeza region.

If seed is to be produced, one very early cutting of hay may be removed first, then 100 to 400 pounds of seed are harvested although as much as 1,500 pounds have been harvested (McKee 1940). If grown only for hay, about 1.5 tons per acre are harvested.

Inflorescence:
The flowers of the lespedezas are of two types: petaliferous (or chasmogamous) and apetalous (or cleistogamous). In the latter, the petals never unfold, so the flower has the appearance of remaining in the bud stage and in which only self-fertilization takes place (Pieters 1934). This characteristic, first noted by Torrey and Gray (1840, pp. 366 - 369), has been studied by various workers. In each type of flower, the ovary has only one ovule. The petaliferous flower is similar to the pea flower - small (l/4 to l/2 inch) with blue to purple petals. The flowers are conspicuous in the shrubby species (fig. 122) but are inconspicuous in most of the herbaceous perennials or annuals (McKee 1948). The apetalous flowers are all inconspicuous.

Hanson (1953a) stated that anthesis or opening of the petaliferous flower occurred from 7 to 10 a.m. The flower is open most of the day, closes before night, and generally does not reopen. In these flowers, the filaments of the nine stamens are fused throughout most of their length. The style extends beyond the anthers, permitting cross-pollination. In the apetalous flowers, the style is J-shaped (Clewell 1964), so that the stigma touches one or more anthers and selfing can occur. Hanson (1953b) stated that the ovary is receptive to fertilization 1 or 2 days before anthesis.

Nectar is apparently secreted at the base of the corolla in the petaliferous flowers because bees visit them freely for both nectar and pollen (Mooers and Ogden 1935, Van Haltern 1936, Graetz 1951, Stitt 1946).

The reason for the development of the two kinds of flowers on lespedeza is unknown. Hanson (1943) concluded that temperature is a strong factor because most of the flowers were apetalous on plants grown at 70deg F, but were petaliferous on plants grown at 80deg. He was of the opinion that other factors also had an effect. There seems to be no information indicating that bees ever visit the apetalous flowers.

[gfx] FIGURE 122. - Flowering branch of bush lespedeza (Lespedeza bicolor).

Pollination Requirements:
Bohart (1960*) reviewed the pollination of the forage legumes and stated that the effect of insect pollinators on seed yields of annual lespedeza has apparently never been investigated. McKee and Hyland (1941) also indicated that there was no information on natural crossing in lespedeza. There is, however, some information on the influence of insect pollination on some of the species.

Stitt (1946) recorded 61.4 to 80.9 percent (average, 70.4 percent) cross-pollination in 'Sericea' which he attributed to the abundant activity of bees. Graetz (1951) showed that L. bicolor, L. japonica, and L. intermedia must be insect pollinated to produce a good seed crop. He stated that 'Sericea' has some flowers that depend on insects and others that self. Donnelly (1955) showed that offspring of 'Sericea' petaliferous flowers produced 25 percent more dry herbage and 40 percent more seeds than the self-pollinated apetalous flowers.

Cope (1966a, b) showed that some 'Sericea' flowers are cross- pollinated by bees and proposed a breeding program of several consecutive generations of inter-crossing for more productive plants. Although he did not go into detail about bee populations on the plants, he noted that 1963 was a poor seed production year for lespedeza, and, correspondingly, the percent crossing was the lowest in years. He recognized the need for bees and conjectured that the "natural bee population" was no longer sufficient to maintain the high level of crossing reported for 'Sericea' two decades ago. He did not consider supplementing the local population by bringing honey bee colonies into the area.

Pieters (1939b) stated that L. striata and L. stipulacea are believed to be self-pollinated. There the matter seems to have rested without further study.

The answer may lie in the fact that honey bees are not strongly attracted to these species (Pellett 1947*), and beekeepers make no effort to place their colonies near lespedeza fields. How the bees might act on the flowers under saturation distribution of colonies, such as is used in the pollination of alfalfa and some other crops, is unknown. The data indicate that floral visitation could be obtained on annual lespedezas if this were sufficiently desired. A study of the beneficial effect of bees on seed production of this crop would be most interesting and is needed.

Pollinators:
Graetz (1951) gave credit to the honey bees for setting the seed obtained in his test on L. bicolor, japonica, and intermedia, but noted that when the honey bees were moved away bumble bees freely visited the flowers. Mooers and Ogden (1935) stated that bees (presumably honey bees) visited the flowers of 'Sericea' for nectar. Cope (1966a, b) referred to the "bees" and the "natural bee population," possibly referring to wild bees on 'Sericea'. Stitt (1946) spoke of "natural crossing" and of usually abundant bees on 'Sericea'. Van Haltern (1936) stated that "bees" visited 'Sericea', L. bicolor, and L. virginica (L.) Britt., and, because he was writing in a beekeeping journal, he doubtless was referring to honey bees.

Beekeepers have generally observed that the lespedezas are scant producers of surplus honey. 'Korean' is rated as the best of the major species, L. bicolor and L. cyrtobotray Miq. are always attractive, although not grown on a large scale anywhere, and 'Kobe' and 'Sericea' are visited at times. Abernathy (1937) stated that lespedeza honey comes largely from 'Korean' with possibly a small amount from 'Common'. Derrenbacker (1936) concluded that bees get little honey from 'Korean'. Pellett (1939, 1952), Taylor (1935), Underhill (1946), and Watson (1938) considered lespedeza only a minor honey plant. Big differences were frequently observed in the populations of the bees on the crop. These differences were associated largely with climate, but location also seemed to be involved.

The evidence indicates that if heavy populations of bees were desired on the commercial lespedezas for pollination purposes they could probably be obtained if honey bee colonies were concentrated in or around the fields. However, the beekeeper would not be compensated for such action in honey storage by the colonies.

Pollination Recommendations and Practices:
The only recommendation for the use of honey bees on lespedeza was by Graetz (1951) who recommended a minimum of one colony per acre in connection with L. bicolor, japonica, and intermedia. Because the perennials appeared to be more attractive species to bees than 'Sericea', it would appear that if honey bees were used on 'Sericea' a higher concentration would be desired. The specific need or value, if any, of bees on 'Common' and 'Koreant lespedezas should be explored.

LITERATURE CITED:
ABERNATHY, E.
1937. LESPEDEZA FOR HONEY. Amer. Bee Jour. 77: 333.

CLEWELL, A. F.
1964. THE BIOLOGY OF THE COMMON NATIVE LESPEDEZAS IN SOUTHERN INDIANA. Brittonia 16(2): 208 - 219.

COPE, W. A.
1966a. CROSS-POLLINATION IN SERICEA LESPEDEZA. Crop Sci. 6: 469-470.

______ 1966b. GROWTH RATE AND YIELD IN SERICEA LESPEDEZA IN RELATION TO SEED SIZE AND OUTCROSSING. Crop Sci. 6: 566.

DERRENBACKER, F., JR.
1936. A REPORT ON LESPEDEZA. Amer. Bee Jour. 76: 402.

DONNELLY, E. D.
1955. THE EFFECTS OF OUTCROSSING ON FORAGE AND SEED YIELDS IN SERICEA LESPEDEZA, L. CUNEATA. Agron. Jour. 47: 466 - 467.

ELROD, J. M.
1954. THE ANNUAL LESPEDEZAS. Ga. Agr. Expt. Sta Press Bul. 651, 2 pp.

ESSARY, S. H.
1921. LESPEDEZA (JAPAN CLOVER). Tenn. Agr. Expt. Sta. Bul. 123, 28 pp.

GRAETZ, K. E.
1951. SHRUB LESPEDEZA REQUIRES INSECT POLLINATION. Soil Conserv. 16: 224-226.

HALTERN, F. VAN.
1936. LESPEDEZA AS A HONEY PLANT. Amer. Bee Jour. 76: 546.

HANSON, C. H.
1943. CLEISTOGAMY AND THE DEVELOPMENT OF THE EMBRYO SAC IN LESPEDEZA STIPULACEA. Jour. Agr. Res. 67: 265 - 272.

HANSON, C. H.
1953a. LESPEDEZA STIPULACEA STAMEN MORPHOLOGY, MEIOSIS, MICROGAMETOGENESIS, AND FERTILIZATION. Agron. Jour. 45: 200 - 203.

______ 1953b. CONTROLLED HYBRIDIZATION IN LESPEDEZA STIPULACEA. Agron. Jour. 45:. 333.

HENSON, P. R., and COPE, W. A.
1969. ANNUAL LESPEDEZAS CULTURE AND USE. U.S. Dept. Agr. Farmers' Bul. 2113, 16 pp.

KINNEY, E. J., and KENNEY, R.
1925. LESPEDEZA IN KENTUCKY. Ky. Agr. Ext. Sen. Cir. 179, 15 pp.

McKEE, R.
1940. LESPEDEZA CULTURE AND UTILIZATION. U.S. Dept. Agr. Farmers' Bul. 1852, 14 pp.

______ 1948. THE LEGUMES OF MANY USES. U.S. Dept. Agr. Yearbook 1948: 701 - 726.

______and HYLAND, H. L.
1941. APETALOUS AND PETALIFEROUS FLOWERS IN LESPEDEZA. Amer. Soc. Agron. Jour. 33: 811-815.

______and PIETERS, A. J.
1937. MISCELLANEOUS FORAGE AND COVER CROP LEGUMES. U.S. Dept. Agr. Yearbook 1937: 999 - 1031.

MOOERS, C. A., and OGDEN, H. P.
1935. LESPEDEZA SERICEA. Tenn. Agr. Expt. Sta. Bul. 154, 19 pp.

PELLETT F. C.
1939. FROM OUR HONEY PLANT GARDENS: BIRDSFOOT TREFOIL, PHACELIA, LESPEDEZA, CLEOME. Amer. Bee Jour. 79: 386.

PELLETT, M. A.
1952. FROM THE HONEY PLANT TEST GARDENS. Amer. Bee dour. 92: 247.

PIETERS, A. J.
1934. THE LITTLE BOOK OF LESPEDEZA. 92 pp. Colonial Press, Washington.

______ 1939a. LESPEDEZA SERICEA AND OTHER PERENNIAL LESPEDEZAS FOR FORAGE AND SOIL CONSERVATION. U.S. Dept. Agr. Cir. 534, 44 pp.

______ 1939b. THE ANNUAL LESPEDEZAS AS FORAGE AND SOIL-CONSERVING CROPS. U.S. Dept. Agr. Cir. 536, 55 pp.

STITT, R. E.
1946. NATURAL CROSSING AND SEGREGATION IN SERICEA LESPEDEZA, LESPEDEZA CUNEATA (DUMONT) G. DON. Amer. Soc. Agron. Jour. 38: 1 - 5.

TAYLOR, D. W.
1935. A FURTHER REPORT FROM VIRGINIA ON LESPEDEZA. Amer. Bee Jour. 75: 572.

TORREY, J., and GRAY, A.
1840. FLORA OF NORTH AMERICA. V. 1, 711 pp. Wiley and Putnam, New York.

UNDERHILL, R.
1946. LESPEDEZA IN ARKANSAS. Amer. Bee Jour. 84: 406.

WATSON, W. E.
1938. LESPEDEZA AGAIN. Amer. Bee Jour. 78: 224.

WHEELER, W. A.
1950. FORAGE AND PASTURE CROPS. 752 pp. D. van Norstrand Co., Inc., New York.

PEANUT
Arachis hypogaea L., family Leguminosae
Peanuts are also known as goobers, groundnuts, and pincers. Approximately 1.5 million acres were planted to peanuts in 1969, and the value of the crop was $311.3 million. This frost-sensitive plant is grown in the southeastern and southern States, primarily for its seed, the peanut, which is a pea and not a true nut. The foliage is sometimes used for livestock feed.

Plant:
The peanut plant is an erect to spreading branched annual, 10 to 20 inches tall, that is cultivated in rows about 1 1/2 to 3 feet apart. The seeds are planted in the spring after all danger of frost is past, and the crop is usually harvested before frost in early fall. The plant has a primary taproot with weak laterals that permit easy removal of the entire plant from the soil. The leaves have four leaflets, 1 1/2 to 2 1/2 inches long. The seeds develop just below the surface of the soil, but they are attached to the branches near the base of the plant.

Inflorescence:
The first flowers appear near the base of each branch, 4 to 6 weeks after planting. Flowering continues along the branch for 6 weeks or more. The peanut flower is yellowish and about one-half inch in size. There may be one to several flowers in an inflorescence on the plant, but only one opens on one day, and there is an interval of one to several days between the opening of successive flowers. Smith (1950) stated that the peanut flower has a recurved beaked keel, with two petals fused along the dorsal edges to the apex but open ventrally at the base. There is a club-shaped stigma on a tortuous style extending beyond the eight functional and two sterile stamens (fig. 146).

The flower opens at sunup and pollen shedding occurs at once, the pollen accumulating between the anthers and stigma. Fertilization occurs 8 to 9 hours after pollination (Oakes 1958). After pollination, the flower fades (Beattie and Beattie 1943), and the ovary elongates to become the peg, which pushes into the soil (fig. 147). In 7 to 10 weeks, the peg matures into the reticulated pod of one to five edible seeds separated by slight constrictions (Gregory et al. 1951).

The value of peanut flowers to bees is not clear. Apparently, there is no functional nectary within the flower although some references indicate (erroneously) that bees collect peanut nectar (Graham 1941*, Pellett 1947*). Pollen is collected by honey bees although peanut plants are not considered to be a major pollen source by beekeepers.

[gfx] FIGURE 146.- Longitudinal section of peanut flower, x 5.
FIGURE 147.- Flower and pegs of a peanut plant.

Pollination Requirements:
There is no doubt that peanuts are largely self-fertilized. The question is whether an increase in the set of seed is caused by cross-pollination. Some selections have a structure that impedes selfing and facilitates cross-pollination by bees. Reed (1924) reported that cross-pollination between cultivars occurs. Kushman and Beattie (1946) and Balhuis (1951) reported finding hybrids in peanuts. Stokes and Hull (1930) pointed out that the stigma of the mature flower " . . . usually lies buried among the dehisced anthers in the tightly closed keel petal so that self-fertilization is assured except for visitation by insects." Srinivasalu and Chandrasekaran (1958) noted that varietal differences exist for cross- pollination in relation to the protrusion of the stigma out of the keel. Leuck and Hammons (1969) reported that two cultivars have a structure in the flower that impedes self-pollination but which facilitates cross- pollination by bees. Leuck and Hammons (1965a) obtained no hybrids from caged plants but got a significant number from plants not caged. Later, they (1965b) reported that at least 80 percent of the peanut flowers in the open were actually tripped for pollen by bees.

Girardeau and Leuck (1967) showed that caged flowers not manipulated in any way produced 4 to 11 percent fewer fruits than hand flexed or water-drip manipulated flowers. Also, their open plots produced a significant 6 to 11 percent more than plots caged to exclude bees. Culp et al. (1968) recorded differences in the amount of crossing that occurred in different areas and in different cultivars but made no mention of the relation of pollinating insects to these differences. Shibuya et al. (1955) associated one-seededness with insufficient pollen on the stigma.

Pollinators:
There seems to be no doubt that the peanut flowe may be cross- pollinated and that crossing is primarily by bees. Hammons and Leuck (1966) showed that thrips are vectors of peanut pollen but that halictid bees were the principal visitors to peanut flowers at Tifton, Georgia. Hammons (1963), at the same location, noted that Lasioglossum, Megachile, Bombus, and Apis species worked peanut flowers. Hammons et al. (1963) and Leuck and Hammons (1969) added Anthidium and Melissodes species to the list of visitors but gave major credit for cross-pollination to species of halictids and megachilids. Diwan and Salvi (1965) stated that Apis cerana generally ignored peanut flowers, but Heide (1923) stated that the flowers were visited "actively and persistently" by A. cerana, and that A. cerana visited the flowers from 7 to 9 p.m. Gibbons and Tattersfield (1969) reported that A. m. adansonii, Nomia spp., and Megachile spp. visited the flowers in the Malawi area of Africa.

Leuck and Hammons (1965b) stated, "We conservatively estimate that in 1964, at least 80 percent of the peanut flowers were actually tripped for pollen each day by species of the combined bee complex." Unfortunately, they gave no indication of the bee population density, floral visitation, or bees per unit of flowers that provided this tripping. Hammons et al. (1963) noted that the halictids and megachilids were most abundant during the cool morning hours when most efficient pollination of peanuts occurs, whereas honey bee activity was spread over the day. No consideration was given to changing the degree of honey bee visitation by concentrating their numbers in the area.

If the 6 to 11 percent increase, which Girardeau and Leuck (1967) attributed to bee pollination, can be consistently obtained, it is of sufficient importance that consideration should be given to building up the bee population of large peanut plantings. This could be done by "saturation pollination" with honey bees if their use could be proven practical.

Pollination Recommendations and Practices:
None.

LITERATURE CITED:
BALHUIS, G. G.
1951. [NATURAL HYBRIDIZATION IN GROUNDNUTS.] Landbouwkundig. Tijdschrift [Wageningen] 63: 447-455. [In Dutch.]

BEATTIE, W. R., and BEATTIE, J. H.
1943. PEANUT GROWING. U.S. Dept. Agr. Farmers' Bul. 1656, 31 pp.

CULP, T. W., BAILEY, W. K., and HAMMONS, R. O.
1968. NATURAL HYBRIDIZATION OF PEANUTS. Crop Sci. 8: 109.

DIWAN, V. V., and SALVI, S. R.
1965. SOME INTERESTING BEHAVIOURAL FEATURES OF APIS DORSATA FAB. Indian Bee Jour. 27(1): 52.

GIBBONS, R. W., and TATTERSFIELD, J. R.
1969. OUT-CROSSING TRIALS WITH GROUNDNUTS (ARACHIS HYPOGAEA L.). Rhodesia Zambia Malawi Jour. Agr. Res. 7: 71-75.

GIRARDEAU. J. H., and LEUCK. D. B.
1967. EFFECT OF MECHANICAL AND BEE TRIPPING ON YIELD OF THE PEANUT. Jour. Econ. Ent. 60: 1454-1455.

GREGORY, W. C., SMITH, B. W., and YARBROUGH, J. A.
1951. MORPHOLOGY GENETICS AND BREEDING. In The PeanutÑthe Unpredictable Legume - a Symposium, pp. 2838, The National Fertilizer Assoc.

HAMMONS, R. O.
1963. ARTIFICIAL CROSS-POLLINATION OF THE PEANUT WITH BEE-COLLECTED POLLEN. Crop Sci. 3: 562-563.

______and LEUCK, D. B.
1966. NATURAL CROSS-POLLINATION OF THE PEANUT, ARACHIS HYPOGAEA L., IN THE PRESENCE OF BEES AND THRIPS. Agron. Jour. 58: 396.

KROMBEIN, K. V., and LEUCK, D. B.
1963. SOME BEES (APOIDEA) ASSOCIATED WITH PEANUT FLOWERING. Jour. Econ. Ent. 56: 905.

HEIDE, F. F. R.
1923. BIOLOGICAL OBSERVATIONS OF ARACHIS HYPOGAEA L. [Dutch East Indies] Alg. Proefsta. v. Landb. Meded. 14: 119.

KUSHMAN, L. J., and BEATTIE, J. H.
1946. NATURAL HYBRIDIZATION IN PEANUTS. Amer. Soc. Agron. Jour. 38: 755.

LEUCK, D. B., and HAMMONS, R. O.
1965a. FURTHER EVALUATION OF THE ROLE OF BEES IN NATURAL CROSS-POLLINATION OF THE PEANUT, ARACHIS HYPOGAEA L. Agron. Jour. 57: 94.

______and HAMMONS, R. O.
1965b. POLLEN-COLLECTING ACTIVITIES OF BEES AMONG PEANUT FLOWERS. Jour. Econ. Ent. 58: 1028-1030.

______and HAMMONS, R. O.
1969. OCCURRENCE OF TYPICAL FLOWERS AND SOME ASSOCIATED BEES (APOIDEA) IN THE PEANUT. ARACHIS HYPOGAEA. Agron. Jour. 61: 958-960.

OAKES. A. J.
1958. POLLEN BEHAVIOR IN THE PEANUT (ARACHIS HYPOGAEA L.) Agron. Jour. 50: 387.

REED, E. L.
1924. ANATOMY, EMBRYOLOGY AND ECOLOGY OF ARACHIS HYPOGAEA. Bot. Gaz.. 78: 289-310.

SHIBUYA. T., SATO, H., and SUZUKI, M.
1955. [MORPHOLOGICAL AND PHYSIOLOGICAL STUDIES ON SUBTERRANEAN FRUCTUATION OF LEGUME CROPS.] Crop Sci. Soc. (Japan) Proc. 24: 16-19. [In Japanese, English summary.]

SMITH B. W
1950. ARACHIS HYPOGAEA. AERIAL FLOWER AND SUBTERRANEAN FRUIT. Amer. Jour. Bot. 37: 802-815.

SRINIVASALU. N., and CHANDRASEKARAN. N. R.
1958. A NOTE ON NATURAL CROSSING IN GROUNDNUT. ARACHIS HYPOGAEA LINN. Sci. Cult. [Calcutta] 23: 650.

STOKES, W. E., and HULL, F. H.
1930. PEANUT BREEDING. Amer. Soc. Agron. Jour. 22: 1004-1019.

PERSIAN CLOVER ³¹
Trifolium resupinatum L., family Leguminosae
__________
³¹ See "Clovers, General."

Persian clover is an annual legume adapted to the heavy low-lying soils of the Southern States from Tennessee southward. It is grown for pasture, for hay, and as a green manure crop. The area, volume, or value of production is not large as compared to other clovers. Not too much has been published on this plant (USDA 1960).

Plant:
The seeds are planted in the fall, and a rosette of leaves is formed during the winter. When spring comes, the upright stems appear and grow rapidly to 8 to 24 inches. They flower and produce seeds in late spring or early summer, then the entire plant dies - somewhat earlier in the season than white clover. The stems do not root at the nodes or creep on the surface, as do many other species of Trifolium, but because they are hollow they lodge badly. Once established, reseeding is unnecessary as seeds are produced in abundance, many of which shatter.

Inflorescence:
The heads are small, pink to light purple, and somewhat flat. They are about the size of those of wild or small white clover and are borne in the leaf axils on 1/2 to 2-inch stems. Honey bees work Persian clover flowers for nectar and pollen (Hollowell 1943). Weaver and Weihing (1960) stated that plants reaching full bloom about April 15 on the gulf coast of Texas still had a considerable amount of bloom on May 7. The flowers of one cultivar were fairly attractive to bees, whereas those of another were seldom visited.

Pollination Requirements:
Lancaster (1949) indicated that Persian clover is not dependent on bees. Hollowell (1943) stated that the flowers are self-fertile and self- pollinating, but honey bees work the flowers for nectar and pollen and undoubtedly help in increasing seed production. Weaver and Weihing (1960) also stated that Persian clover does not require insect pollination, but their caged plots that included bees yielded about nine times as much seed as plots caged without bees. Wheeler and Hill (1967*) also indicated that bees increase seed production. The degree of help is not clear, but the small amount of data available indicate that bees are highly beneficial and that they should be used if maximum seed production is desired.

Pollinators:
The meager evidence available indicates that honey bees are the principal pollinators of Persian clover. Weaver and Weihing (1960) stated that Persian clover yielded "little nectar per blossom, but the bees foraged from the individual florets very rapidly," which helped to compensate for the small amount of nectar.

Pollination Recommendations and Practices:
The number of colonies per acre or bees per square yard of Persian clover to provide maximum benefit has not been determined. The desired concentration of bees is probably similar to that for crimson clover.

LITERATURE CITED:
HOLLOWELL, E. A.
1943. PERSIAN CLOVER U. S. Dept. Agr. Farmers' Bul. 1929, 10 pp.

LANCASTER, R. R.
1949. CLOVERS FOR TEXAS PASTURES. Tex. Agr. Ext. Serv. Pub. B-168, 24 pp.

UNITED STATES DEPARTMENT OF AGRICULTURE.
1960. PERSIAN CLOVER- A LEGUME FOR THE SOUTH. U. S. Dept. Agr. Leaflet 484, 8 pp.

WEAVER, N., and WEIHING R. M.
1960. POLLINATION OF SEVERAL CLOVERS BY HONEY BEES. Agron. Jour. 52: 183185.

RED CLOVER ³³
Trifolium pratense L., family Leguminosae
Red clover is a highly important forage legume, although much of the acreage formerly in red clover has been diverted to alfalfa growing. The acreage in red clover seed production has dropped from over 2 l/2 million acres in 1950 to about 1/2 million acres per year for 1967-71.

The principal seed-growing area is the Central and North Central States, although highest per acre production is in the Western States. In 1969, production in the four Western States, California, Idaho, Oregon, and Washington, ranged from 305 to 410 pounds per acre, with Oregon fourth in total production of clean seed. Michigan (5.5 millions pounds), Indiana (5.2 million pounds), and Illinois (5 million pounds) lead in total seed produced. These seven States produced more than half of the 43.9 million pounds.

E. A. Hollowell (personal commun., 1971) expressed the belief that red clover will be used more in the future than it is at present. This, he believed, was because farmers had concentrated on production of high- priced corn and soybean crops and had long neglected a crop rotation program to replenish the soil. He believed that with the inevitable return to such a program, red clover will regain its popularity.

Red clover is a short-life herbaceous perennial plant that grows to a height of 15 to 36 inches. It is easily recognized by its fine leafy stems, its trifoliate leaves, and rose-pink oval flower heads that are 1 to 1 l/2 inches in diameter (fig. 168). When the crop is harvested for hay, the plants are cut during early bloom. If seed is desired, the plants are usually left after a first cutting, until all of the seed heads are mature.
__________
³³ See "Clovers, General."

[gfx] FIGURE 168. - Red clover blossoms.

Inflorescence:
The compact flower head, borne on the tip of the branch or stem, is made up of 55 to 275 florets (Williams 1930), which open over a period of 6 to 8 days from the base toward the top (Pammel and King 1911). An acre of red clover in full bloom will have an estimated 300 million florets (Hollowell and Tysdal 1948). (There are 250,000 or more seeds per pound.) Depending on the vigor of the plant, the floret may be 1/4 to l/2 inch long (7.5 to 12.4 mm) but only 1/12 inch in diameter (1.6 to 2.5 mm) (Akerberg 1953, Dennis and Haas 1967b). Within the ovary of the floret are two ovules, but rarely more than one develops. Dijkstra (1969) showed that when two-seededness occurred it had no influence on total seed yield. The staminal column, with its 10 stamens and the slightly longer stigma, extends to the mouth of the corolla tube, but is enclosed within the keel petals. When the bee exerts pressure with its head on the keel petals, the stigma and the anthers are excerted or "tripped" and come in contact with the bee, usually on the posterior part of the head (Woodrow 1952b ). When the pressure is removed the staminal column returns to its former position within the keel, but can be tripped repeatedly.

Nectar is secreted at the base of the corolla tube but only extends 1.35 to 1.47 mm up the tube. Tetraploid red clover produces more nectar per floret than diploid, but because of the longer corolla tube the nectar is no more accessible to the honey bee (Dennis and Haas 1967b), which has a "tongue" or proboscis length of only 5.90 to 6.25 mm (McGregor 1938). Thus, only with the shortest corolla tube (7.5 mm) filled to the highest (1.5 mm) would the 5.90 to 6.25 mm honey bee tongue reach the red clover nectar. Hawkins (1969) stated that the honey bee can reach to a depth of 7 mm in the corolla tube. Dennis and Haas (1967b) stated that the honey bee is able to push its head about 1.4 mm into the corolla tube thereby increasing the effective length of the tongue (fig. 169). It is well known that the corolla tube of late-season red clover is usually much shorter than at the first flowering. Although surplus red clover honey production is uncommon, beekeepers frequently report that bees work red clover late in the season. Holm (1972) caused a reduction in corolla tube length by spraying the plants with a growth retarding chemical. This resulted in a higher frequency of honey bee visits and increased seed production on the treated plants.

Bukhareva (1960) showed that nectar secretion was influenced by plant nutrients. Plots treated with 8 oz boron and 3 oz ammonium molybdate showed a 53 percent increase in nectar secretion, 7 to 11 percent increase in sugar concentration, 17 to 32 percent increase in bee visitation, and 14 to 15 percent increase in seed production. Killinger and Haynie (1961) associated lack of boron with low seed yields in Florida. Unfortunately, too little attention has been paid to the influence of soil nutrients on floral attractiveness of red clover as well as on many other plants.

MacVicar et al. (1952) obtained no benefit from spraying plots with dilute honey to attract honey bees, and, in general, the baiting of bees into the field has not proven practical in the United States.

Hawkins (1969) showed that the corolla varied considerably in length, and he believed that the development of either short corolla strains of red clover or long-tongued bees might be feasible. He also believed that breeding clover cultivars with more nectar would contribute to better pollination. Akerberg et al. (1966) found that, in general, the corolla tubes were shorter towards southern Europe than to the north, an indication that location of growth might influence bee visitation.

There seems to be no question that some species of bumble bees can reach the red clover nectar with ease. Under certain conditions, all species of bumble bees and honey bees can reach the nectar (Bond 1968, Bond and Fyfe 1968).

Woodrow (1962a) concluded that the "depth of the red clover corolla in relation to the length of the honey bee's tongue appears to be unimportant to mechanics of the pollination act," because the tongue plays no part in the transfer of pollen. The question then becomes one of the degree of visitation by the honey bee if it were not rewarded with nectar. Woodrow (1952a) believed that most of the honey bee visits to red clover were for pollen, although some bees collected nectar also. Bond (1968) showed that tetraploid red clover produced more nectar than related diploid cultivars, but the nectar was lower in the corolla tube and more difficult for honey bees to reach.

Specific races of honey bees have been mentioned by various writers as being better pollinators of red clover than other races (Alpatov 1946, 1948; Smaragdova 1956; and Hammer 1950). There is no agreement as to which race is superior in this regard, and no recent attempt has been made to breed such a bee. In the late 1890's, beekeepers made attempts to select superior red clover honey-producing bees but failed. However, Stahlin and Bommer (1958) concluded that breeding clover to suit the bees would be more profitable than breeding bees to fit the clover. Starling et al. (1950) concluded that short corollas alone offered no advantage for increased seed production.

Woodrow (1952b) described in detail the method the honey bee follows in pollinating red clover. He stated that the length of the tongue of the bee need be no handicap in pollination of this flower because the sexual parts of the flower are at the tips, and the bee's tongue is not used in transferring pollen from flower to flower.

[gfx] FIGURE 169. - Bee head (enlarged) with proboscis extended into red clover bloom.

Pollination Requirements:
The pollination of red clover has probably been more extensively studied than that of any other plant, not only in the United States but also in many other countries. Excellent reviews have been made by Bohart (1957, 1960 *), Dennis and Haas (1967a, b), Free (1970*), Gubin (1947), Stahlin and Bommer (1958), and Umaerus and Akerberg (1959). The discussion on red clover pollination by Free (1970*) is extensive and thorough. Krishchunas and Gubin (1956) also devoted about 25 pages of their book to this crop.

Self-sterility in red clover has been known since Darwin (1889*) showed that caged plants would not set seed unless they were cross- pollinated. The pollen must come from another plant if commercial production of seed is anticipated (Williams 1931, Westgate and Coe 1916). Martin (1913) demonstrated that self-pollen tubes penetrated the style toward the ovary more slowly than foreign pollen (from another red clover plant). Whether or not this time factor is critical has not been demonstrated, but the floret must be pollinated within 2 to 4 days after it opens (Free 1965, Umaerus and Akerberg 1959). The appearance of the flower heads is a strong clue to the adequacy of pollination. If pollination does not occur, the florets remain turgid, the head is soon covered with the colorful florets, and the field takes on a flower-garden appearance.

If pollination is adequate, an individual head in flower will have the lower florets pollinated and wilted, with the position of the florets changed from upright to drooping, the color changed from rose-pink to rusty brown, those in the center of the head attractive to pollinators, and the uppermost ones still in the bud stage (Woodrow 1952a). When this situation exists, the field takes on a greenish-brown cast. Naturally, the seed-grower should strive for this situation and should be concerned if the field has the flower-garden appearance.

Pollinators:
The relative value of the pollinating insects on red clover has been debated for decades. Many references attest to the value of bumble bees. Others support honey bees, and some support other genera of bees. Hawkins (1962a) found a correlation between bumble bee populations and red clover seed production in England 2 years out of 3, but no correlation between honey bees and seed production. He (1962b) proposed that an organization be formed to make annual counts of bumble bees, similar to bird counts, to stimulate public interest in these insects. Bird (1944) also considered bumble bees much more important than honey bees.

Lindhart (1911) concluded that honey bees occasionally aid in red clover pollination. This evaluation of honey bees has consistently increased over the years in many subsequent papers. For example, Anderson and Wood (1944) obtained one seed per head of red clover where bees were excluded but 56 seeds per head where honey bees were caged on the plants.

Butler (1941), Valle (1959), and Valle et al. (1960) after thorough studies gave credit to both honey bees and bumble bees. The other genera of bees that have been mentioned, but in general considered of little importance, include Andrena (Benoit et al. 1948), Eucera (Yamada and Ebara 1952), Halictus (Maurizio and Pinter 1961), Megachile (Akerberg et al. 1966), Melissodes (Folsom 1922), Osmia (Maurizio and Pinter 1961, Akerberg et al. 1966), Psithyrus (Sculler 1930), and Tetralonia [Synhalonia] (Folsom 1922).

Dennis and Haas (1967b) also observed the action of bumble bees on red clover and learned that Bombus terrestris (L.), with a short (6.8 mm) tongue, obtained red clover nectar only by cutting a hole in the base of the corolla tube. B. lapidarius (L.), with an 8-mm tongue, collected nectar normally from diploid red clover. B. distinguendus F. Morawitz, with an 8.8-mm tongue, and B. hortorum (L.) (11.1 mm) were more frequent on tetraploid red clover.

Bohart (1957) and van Laere and Martens (1962) concluded that bumble bees, except for a few nectar-thieving species, are ideal pollinators of red clover although their populations are unpredictable and usually insufficient to adequately pollinate all the blossoms in a large field. Bohart (1957) considered honey bees satisfactory if they are sufficiently concentrated in the area and the competing pollen and nectar sources are kept at a minimum. In Canada, Peterson et al. (1960) also concluded that honey bees were best. In Russia, Gubin (1947) considered bumble bees to be the best pollinators of red clover on a bee-for-bee basis but that overall they provided only 3.5 percent of the pollination service. The value of honey bees was expressed by Hopkins (1896a, b), Pieters (1924), and Stapel (1934) and demonstrated by Richmond (1932), Dunham (1932, 1939a, b, c), and Armstrong and Jamieson (1940a, b).

Bumble bees were considered of such importance that they were transported from England and established in New Zealand for the express purpose of pollinating red clover (Belt 1876, Hopkins 1914). However, Forster and Hadfield (1958) showed that 35 colonies of honey bees placed adjacent to a 10-acre field of Montgomery red clover in New Zealand provided 77 percent of the pollinating insects in 1954 and 89 percent in 1955. They stated that this was a fair cross-section of pollinator activity on red clover crops in South Canterbury. Morrison (1961) found inconsistencies over the years between the efficiency of honey bees and bumble bees in New Zealand and considered both groups of value. Hills (1941), Palmer-Jones et al. (1966), and Palmer-Jones (1967) considered honey bees of greater value than bumble bees. Bond and Fyfe (1968) showed that seed production in a cage with one strong colony of bees was more than twice that in a cage with a weak colony.

Hollowell (1932) proposed the introduction of additional honey bee colonies into clover fields to increase seed production. This action has now become a common practice. Walstrom et al. (1951a, b) proposed 400- to 600-foot intervals as an economical distance between groups of colonies used for red clover pollination. Jamieson (1955) showed that only 63 lb/acre of seed were obtained with local wild bees, but 307 lb/acre were obtained with two colonies of honey bees per acre.

The production of red clover seed is directly proportional to pollinator activity. Everly (1950) associated reduced native pollinators with decreased seed yields in Indiana, and stated that red-clover pollen- collecting honey bees were effective in setting a good crop of seed. Walstrom et al. (1951a, b) showed that seed production decreased 6.4 lb/acre with each 100 feet of distance from the apiary. Walstrom (1958) showed that differences in seed yields at 100-foot intervals from apiary sites were significant at the 1-percent level of probability. Zivov and Skvorcov (1951) also showed that seed production decreased with increased distance: 246 lb/acre when the field was only 0.5 km from the bee source, 158 lb/acre at 1 to 1.5 km, and only 90 lb/acre beyond 1.5 km. Jamieson (1956) obtained 307 lb/acre with two colonies per acre but only 63 lb/acre when honey bees were not provided. Thomas (1961) and Braun et al. (1963) obtained similar results.

The data leave little doubt that if bumble bees are not sufficiently abundant (and they usually are not), their services can be supplemented and seed production stabilized by the use of honey bees. Other pollinators are of little significance.

Pollination Recommendations and Practices:
Hogborg (1966) considered pollinators in terms of "positive bee pollinating units," and calculated that adequate pollination would be given by 20,000 units per hectare (using the value of 2.5 units for one bumble bee). This amounts to about one bumble bee or two nectar-collecting honey bees per square yard. Akerberg (1947) calculated that 1,100 bumble bees per hectare (about 0.1 bee/yd² ) were sufficient to produce 300 kg alfalfa seed per hectare (about 300 lb/acre). These estimates are below the amounts specified in the formula of Stanley Roadfeldt (McGregor 1966) of one honey bee per 4 yd2 per minute equals 300 pounds red clover seed, or one bee per square yard per minute equals 700 pounds red clover seed.

Dennis and Haas (1967a) used a numerical rating on the values of bees on diploid red clover, based on the bees' working speed, as follows:

[gfx] fix table:

Apis.................................................................................................1.0 Short-tongued Bombus .........................................................1.5 Long-tongued Bombus............................................................2.5 However, their remanipulated data gave the following values: Nectar-collecting honey bee ................................................1.0 Pollen -collecting honey bee ...............................................1.3 Nectar-collecting bumble bee .............................................1.6 Pollen-collecting bumble bee ..............................................1.9

By this method, they considered pollen-collecting, long-tongued bumble bees to be about twice as efficient as honey bees.

The pollination recommendations for red clover revolve around bumble bees and honey bees. The presence of bumble bees can be encouraged by providing them with domiciles, by protecting them from pesticides (rye and Medler 1964, Hobbs 1967, Holm 1966), and by planting off-season flowering plants to provide nectar and pollen. Honey bee colonies can be transported and placed in or adjacent to red clover fields in any number desired and when desired. This is a more dependable practice than "encouraging" the bumble bees.

In most cases, the number of colonies of honey bees that has been recommended per acre has ranged from one to three, but a few recommendations have mentioned four, five, six, and up to 10 colonies per acre. Some urge that the colonies be placed adjacent to the field, others recommend that the colonies be placed within the field in groups of 10 or more 100 to 400 yards apart. Some recommendations stress bees per square yard, the number of bees ranging from 1 to 18. The use of strong colonies is urged. E. A. Hollowell (personal commun., 1971) stated that two bees per square foot (18 per square yard) should set an abundant seed crop. This may require the use of several strong colonies per acre.

If visitation in the field is adequate, the field will have a rusty- brown hue instead of the rose-colored flower-garden appearance. The number of colonies of honey bees per acre necessary to provide this visitation will vary with condition of the colonies, placement pattern, climate, crop, and competing plants. The important point to remember is that there should be sufficient bees on the flowers to keep the florets tripped as rapidly as they appear.

LITERATURE CITED:
AKERBERG, E.
1947. [SOME ACTUAL PROBLEMS IN THE BREEDING OF RED CLOVER AND ALFALFA FOR CENTRAL SWEDEN.] Sartryck ur Sveriges Utsadesforenings Tidskrift 1947, Hafte 3, 19 pp. [In Swedish, English summary.]

______ 1953. [FLORAL BIOLOGY AND POLLINATION OF RED CLOVER.] Pp.16-33. In [Investigations of Insect Pollinated Crops. II. Studies on Red Clover Seed Production. Results of Experiments made during 1942-1952.] Swedish Seed Growers Assn., Medd. 2. [In Swedish.]

STAPEL, S., and STAPEL, C.
1966. A SURVEY OF POLLINATION AND SEED GROWING OF RED CLOVER IN EUROPE. In Internatl. Symposium on Pollination, London, 1964. Bee World 47 (supp.): 15 - 42.

ALPATOV, V. V.
1946. [INTRASPECIFIC DIFFERENCES OF THE HONEY BEE IN PLANT POLLINATION.] Bul. soc. Nat. Moscow, S. Biologique, T. 51(3): 54-62. [In Russian.]

______ 1948. BEE RACES AND RED CLOVER POLLINATION. Bee World 29(8): 61-63.

ANDERSON, E. J., and WOOD, N.
1944. HONEYBEES AND RED CLOVER POLLINATION. Amer. Bee Jour. 86: 156-157.

ARMSTRONG, J. M., and JAMIESON, C. A.
1940a. RED CLOVER AND HONEYBEES. Canad. Bee Jour. 48(12): 301-304.

______and JAMIESON, C. A.
1940b. CROSS-POLLINATION OF RED CLOVER BY HONEY BEES. Sci. Agr. 20: 574-585.

BELT, T.
1876. BEES AND CLOVER. Nature 13: 26.

BENOIT, P., GILLARD, A., and BRANDE, J. VAN DEN.
1948. [CONTRIBUTIONS TO THE STUDY OF THE FERTILIZATION OF RED CLOVER IN RELATION TO SEED PRODUCTION.] Med. Lantbr. Hogsk. Gent 13: 297-346. [In Swedish, English summary.]

BIRD, J. N.
1944. SEED SETTING IN RED CL0VER. Amer. Soc. Agron. Jour. 36: 346-357.

BOHART, G. E.
1957. POLLINATION OF ALFALFA AND RED CLOVER. Ann. Rev. Ent. 2: 355-380.

BOND, D. A.
1968. VARIATION BETWEEN TETRAPLOID RED CLOVER PLANTS IN COROLLA TUBE LENGTH AND HEIGHT OF NECTAR. Jour. Agr. Sci. (Cambridge) 71: 113-116.

______and FYFE, J. L.
1968. COROLLA TUBE LENGTH AND NECTAR HEIGHT OF F₁ RED CLOVER PLANTS. Jour. Agr. Sci. (Cambridge) 70(pt.1): 5-10.

BRAWN, E., MACVICAR, R. M., GIBSON, D. R., PANKIW, P., and others.
1953. STUDIES IN RED CLOVER SEED PRODUCTION. PART II. Canad. Jour. Agr. Sci. 33: 437-447.

BUKHAREVA, G. A.
1960. [TRACE ELEMENTS AND RED CLOVER.] Pchelovodstvo 37(3): 15-17. [In Russian.] AA-137/63

BUTLER, C. G.
1941. A STUDY OF THE FREQUENCY WITH WHICH HONEYBEES VISIT RED CLOVER. Ann. Appl. Biol. 28(2): 125-134.

DENNIS, B. A., and HAAS, H.
1967a. POLLINATION AND SEED-SETTING IN DIPLOID AND TETRAPLOID RED CLOVER (TRIFOLIUM PRATENSE L.) UNDER DANISH CONDITIONS. I. SEEDSETTING IN RELATION TO THE NUMBER AND TYPE OF POLLINATING INSECTS. Roy. Vet. and Agr. Col., Copenhagen, Yearbook 1967: 93-117.

______and HAAS, H.
1967b. POLLINATION AND SEED-SETTING IN DIPLOID AND TETRAPLOID RED CLOVER (TRIFOLIUM PRATENSE L.) UNDER DANISH CONDITIONS. II. STUDIES OF FLORET MORPHOLOGY IN RELATION TO THE WORKING SPEED OF HONEY AND BUMBLE-BEES (HYMENOPTERA: APOIDAE). Roy. Vet. and Agr. Col., Copenhagen, Yearbook 1967: 118-133.

DIJKSTRA, J.
1969. THE IMPORTANCE OF TWO-SEEDED PODS OF RED CLOVER (TRIFOLIUM PRATENSE L.). Euphytica 18: 340-351.

DUNHAM, W. E.
1932. VALUE OF HONEYBEES IN POLLINATING RED CLOVER. Gleanings Bee Cult. 60: 614-616.

______ 1939a. COLLECTING RED CLOVER POLLEN BY HONEYBEES. Jour. Econ. Ent. 32: 668-670.

______ 1939b. HONEY BEES NEEDED TO POLLINATE RED CLOVER. Pa. Beekeeper 13(4): 6-7.

______ 1939c. INSECT POLLINATION OF RED CLOVER IN WESTERN OHIO. Gleanings Bee Cult. 67: 486-488, 525.

EVERLY, R. T.
1950. LEGUME POLLINATION PROBLEMS. Ind. Acad. Sci. Proc. 59: 164-172.

FOLSOM, J. W.
1922. POLLINATION OF RED CLOVER BY TETRALONIA AND MELISSODES. Ent. Soc. Amer. Ann. 15: 181-184.

FORSTER, I. W., and HADFIELD, W. V.
1958. EFFECTIVENESS OF HONEY BEES AND BUMBLE BEES IN THI POLLINATION OF MONTGOMERY RED CLOVER. New Zeal. Jour. Agr. Res. 1: 607-619.

FREE, J. B.
1965. THE ABILITY OF BUMBLEBEES AND HONEYBEES TO POLLINATE RED CLOVER. Jour. Appl. Ecol. 2: 289-294.

FYE, R. E. and MEDLER, J. T.
1951. FIELD DOMICILES FOR BUMBLEBEES. Jour. Econ. Ent. 47: 672-676.

GUBIN, A. F.
1947. HONEY BEES AND THE POLLINATION OF RED CLOVER.] Moskva, Sel'khozgiz, 277 pp. [In Russian, English summary. ]

HAMMER, O.
1950. BEES DO WORK RED CLOVER - EXPERIMENTS IN DENMARK PROVE. Canad. Bee Jour. 58(10): 4-14.

HAWKINS, R. P.
1962a. BEES IN RELATION TO SEED CROPS FROM RED CLOVER. Bee World 43: 114-119.

______ 1962b. POLLINATION OF RED CLOVER BY BEES. In 1st Internatl. Symposium on Pollination Proc., Copenhagen, Aug. 1960. Commun. 7, Swedish Seed Growers' Assoc., pp. 30-37.

______ 1969. LENGTH OF TONGUE IN A HONEY BEE IN RELATION TO THE POLLINATION OF RED CLOVER. Jour. Agr. Sci. (Cambridge) 73: 489-493.

HILLS, K. L.
1941. RED CL0VER SEED PRODUCTION AT MOSS VALE, N.S.W. AUSTRALIA. Austral. Council Sci. and Indus. Res. Jour. 14: 249-252.

HOBBS, G. A.
1967. OBTAINING AND PROTECTING RED-CLOVER POLLINATING SPECIES OF BOMBUS (HYMENOPTERA: APIDAE). Canad. Ent. 99: 943-951.

HOGBORG, E.
1966. [BUMBLE BEES AND HONEY BEES AS POLLINATORS IN DIPLOID RED CLOVER.] Lantbr. Hogsk. Meddel. (A), No. 47, 52 pp. [In Swedish, English summary.]

HOLLOWELL, E. A.
1932. RED-CLOVER SEED PRODUCTION IN THE INTERMOUNTAIN STATES. U.S. Dept. Agr. Leaflet 93, 7 pp.

______and TYSDAL, H. M.
1948. THE NEED FOR SEED IS URGENT. U.S. Dept. Agr. Yearbook 1948: 341-346.

HOLM, S. N.
1966. THE UTILIZATION AND MANAGEMENT OF BUMBLE BEES FOR RED CLOVER AND ALFALFA PRODUCTION. Ann. Rev. Ent. 11: 155-182.

______ 1972. SEED YIELDS IN RED CLOVER IN RELATION TO THE NUMBER OF POLLINATING BEES AS INFLUENCED BY A GROWTH REGULATOR. Roy. Vet. and Agr. Univ. Yearbook, Copenhagen, pp. 127-141.

HOPKINS, A. D.
1896a. ON THE FLOWERING HABITS OF TIMOTHY AND RED CLOVER AND THE POLLENIZATION OF THE FLOWER BY INSECTS. In 17th Mtg. of the SOC. for Promotion of Agr. Sci. Proc.: 35-40. Buffalo, N,Y.

______ 1896b. SOME NOTES ON OBSERVATIONS IN WEST VIRGINIA ON FARM, GARDEN AND FRUIT INSECTS. U.S. Dept. Agr., Div. Ent. Bul. 6, n.s., pp. 71-73.

HOPKINS I.
1914. HISTORY OF THE BUMBLEBEE IN NEW ZEALAND - ITS INTRODUCTION AND RESULTS. New Zeal. Dept. Agr. lndus., and Com. Bul. 46, n.s., 29 pp.

JAMIESON, C. A.
1955. PROGRESS REPORT, 1949 - 1953. 41 pp. Apiculture Division, Dominion Expt. Farm, Ottawa, Canada.

KILLINGER, G. B., and HAYNIE, J. D.
1951. HONEYBEES IN FL0RIDA'S PASTURE DEVELOPMENT. Fla. Dept. Agr. Bul. (Spec. Serv.) 66: 112-115.

KRISHCHUNAS, I. V., and GUBIN, A. F.
1956. [POLLINATION OF AGRICULTURAL PLANTS.] 231 pp. MoskVa, Gos. Izd-vo Selkhoz Lit-ry. [In Russian.]

LAERE, O. VAN, and MARTENS, N.
1962. [THE IMPORTANCE OF THE DOMESTIC BEE IN THE PRODUCTION OF RED-CLOVER (TRIFOLIUM PRATENSE) SEED.] Rev. del'Agr. 15(11/12): 1383-1395. [In French, English conclusions.]

LINDHARD, E.
1911. [POLLINATION OF RED CLOVER BY BUMBLEBEES.] Tidsskrift for Landbruets Planteavel. 18(5): 719 - 737. [In Danish.]

MACVICAR, R. M., BRAWN, E., GIBSON, D. R., and JAMIESON, C. A.
1952. STUDIES IN RED CLOVER SEED PRODUCTION. Sci. Agr. 32: 67-80.

MARTIN, J. N.
1913. THE PHYSIOLOGY OF THE POLLEN OF TRIFOLIUM PRATENSE. Bot. Gaz. 56: 112-126.

MAURIZIO, A., and PINTER, L.
1961. [OBSERVATIONS ON NECTAR SECRETION AND INSECT VISITATION OF A FEW FIELD VARIETIES OF SWISS RED CLOVER (TRIFOLIUM PRATENSE L.).] In Arbeiten aus dem Gebiete des Futterbaues: 41-46. Zurich- Oerlikon, Arbeitsgemeinschaft zur Forderung des Futterbaues (AGFF). [In German.] AA-462/62.

MCGREGOR, S. E.
1938. ENVIRONMENTAL FACTORS AND SIZE VARIATIONS IN HONEYBEE APPENDAGES. Jour. Econ. Ent. 31: 570 - 573.

______ 1966. SUMMATION OF THE 7TH BEE POLLINATION CONFERENCE, COLLEGE STATION, TEXAS, OCTOBER 1,1965. Amer. Bee Jour. 106: 8-9, 17.

MORRISON, L.
1961. POLLINATION AND SEED-SETTING OF RED CLOVER IN SCRIM- COVERED CAGES. New Zeal. Jour. Agr. Res. 4(5/6): 560-565.

PALMER-JONES, T.
1967. HONEY BEES AS POLLINATORS OF RED CLOVER. New Zeal. Jour. Agr. 114: 34-35.

______FORSTER, I. W., and CLINCH, P. G.
1966. OBSERVATIONS ON THE POLLINATION OF MONTGOMERY RED CLOVER (TRIFOLIUM PRATENSE L.). New Zeal. Jour. Agr. Res. 9(3): 738-747.

PAMMEL, L H., and KING, C. M.
1911. POLLINATION OF CLOVER. Iowa State Col. Bot. Dept. Contrib. 47: 36-45.

PETERSON, A. G., FURGALA, B., and HOLDAWAY, F. G.
1960. POLLINATION OF RED CLOVER IN MINNESOTA. Jour. Econ. Ent. 53: 546-550.

PIETERS, A. J.
1924. RED CLOVER CULTURE. U.S. Dept. Agr. Farmers' Bul. 1339, 30 pp.

RICHMOND, R. G.
1932. RED-CLOVER POLLINATION BY HONEYBEES IN COLORADO. Colo. Agr. Expt. Sta. Bul. 391, 22 pp.

SCULLEN, H. A.
1930. NOTES ON THE DISTRIBUTION AND ALTITUDE RANGE OF OREGON BREMIDAE (HYMENOPTERA). Jour. Econ. Ent. 23: 786-789.

SMARAGDOVA, N. P.
1956. [SELECTIVE ABILITY OF BEES IN POLLINATING PLANTS.] Uchen. Zap. Moskov. gos. Univ. (183): 97-102. [ In Russian. ] AA-394/60.

STAHLIN, A., and BOMMER, D.
1958. [METHODS OF IMPROVING FERTILIZATION OF RED CLOVER.] Angew. Bot. 32(5): 165-185. [In German.]

STAPEL, C.
1934. [HONEYBEES AND RED CLOVER SEED PRODUCTION.] Tidsskr. Lor Planteavl. 40: 301-313. [In Danish]

STARLING, T. M., WlLSIE, C. P., and GILBERT, N. W.
1950. COROLLA TUBE LENGTH STUDIES IN RED CLOVER. Agron. Jour. 42: 1-8.

THOMAS, W.
1951. BEES FOR POLLINATING RED CLOVER. Gleanings Bee Cult. 79: 137-141.

UMAERUS, M., and AKERBERG, E.
1959. POLLINATION AND SEED SETTING IN RED CLOVER AND LUCERNE UNDER SCANDINAVIAN CONDITIONS. Herbage Abstracts 29(3): 157-164, 1959.

VALLE, O.
1959. POLLINATION AND SEED SETTING IN TETRAPLOID RED CLOVER IN FINLAND. Suomen Maataloustieteellisen Seuran Julkaisuja 95(4): 1-32.

______SALMINEN, M., and HUOKUNA, E.
1960. POLLINATION AND SEED SETTING IN TETRAPLOID RED CLOVER IN FINLAND. II. Suomen Maataloustieteellisen Seuran Julkaisuja 97(1): 1-62.

WALSTROM, R. J.
1958. EFFECTS OF FLIGHT DISTANCES FROM HONEY BEE COLONIES ON RED CLOVER SEED YIELDS. Jour. Econ. Ent. 51: 64-67.

______PADDOCK, F. B., PARK, O. W., and WILSIE, C. P.
1951a. RED CLOVER POLLINATION AT VARIOUS DISTANCES FROM HONEY BEE COLONIES. In lowa State Apiarist Rpt. 1950. Pp. 51-52.

______PADDOCK, F. B., PARK, O. W., and WILSIE, C. P.
1951b. RED CLOVER POLLINATION. Amer. Bee Jour. 91: 244-245.

WESTGATE, J. M., and COE, H. S.
1915. RED CLOVER SEED PRODUCTION: POLLINATION STUDIES. U.S. Dept. Agr. Bul. 289: 17-18.

WILLIAMS, R. D.
1930. SOME OF THE FACTORS INFLUENCING YIELD AND QUALITY OF RED CLOVER SEEDS. Welsh Plant Breed. Sta., Aberystwyth, Bul. Ser. H. 11: 60-91.

______ 1931. SELF- AND CROSS-STERILITY IN RED CLOVER. Welsh Plant Breed. Sta., Aberystwyth, Bull Ser. H. 12: 181-208.

WOODROW, A. W.
1952a. EFFECT OF TIME OF POLLINATION BY HONEY BEES ON RED CLOVER SEED YIELDS. Jour. Econ. Ent. 45: 517-519.

______ 1952b. POLLINATION OF THE RED CLOVER FLOWER BY THE HONEY BEE. Jour. Econ. Ent. 45: 1028-1029.

YAMADA, I., and EBARA, K.
1952. [STUDIES ON THE FERTILIZATION OF RED CLOVER TRIFOLIUM PRATENSE, BY BUMBLE BEES AND HONEY BEES.] Hokkaido Nat. Agr. Expt. Sta. Rpt. No. 45, 33 pp. [ln Japanese, English summary.]

ZIVOV, V., and SKVORCOV, S.
1951. [METHODS OF IMPROVING POLLINATION OF CLOVERS BY HONEY BEES.] Selek. i Semen. 18(6): 63-64. [In Russian.] Abstract in Herbage Abstracts 22(2): 86-87.

ROSE CLOVER³⁴Trifolium hirtum All., family Leguminosae
Rose clover is grown primarily in California, where it is used for seeding brush burns, cleared brushland, and dryland pasture. It will grow in dry "sterile" fields, on slopes, sandy steppes, or roadsides, and in waste places. Cattle and sheep, as well as such wildlife as deer, doves, and quail feed upon it even when it is completely dried up (Arkley et al. 1955, Holland 1964, Love and Sumner 1952, Williams et al. 1957).
__________
³⁴ See "Clovers, General."

Plant:
Rose clover is a reseeding annual winter legume. The leaflets usually have a small reddish mark near or slightly above the center (Strang and Broue 1958). The leaf stalks are 1/2 inch to 2 inches long. The seeds germinate with the first substantial fall rain and the plant grows slowly as a rosette of leaves until late winter. Then, as spring temperatures rise, it grows rapidly into an upright many-branched plant 3 to 18 inches tall. It blooms and sets seed in May. The plant then becomes dry and casts its seeds, which ripen 4 to 6 weeks after flowering starts. The seeds remain dormant in the soil until fall rains begin (Bailey 1966, Williams and Leonard 1959). Rose clover provides a high-quality forage pasture under a wide variety of climatic conditions in California. Plantings succeed in areas with as little as 10 inches of rainfall. Foliage of rose clover is much less profuse than most other clovers. It has the ability to produce some seeds under extremely unfavorable conditions (fig. 170).

[gfx] FIGURE 170. - Rose clover in bloom.

Inflorescence:
The pink flower head of rose clover is spherical, about three- quarters of an inch across, and profusely covered with stiff white hairs. These blossoms are highly attractive to bees for both nectar and pollen. When a floret is visited by a bee, the staminal column protrudes, then withdraws after the bee departs. From four to six bees per square yard have been seen on this plant. There is one seed per floret, and there are 40 florets per head.

Pollination Requirements:
Bohart (1960*) stated, "In California, honey bees are sometimes placed by fields of rose clover to ensure pollination, but apparently the practice is not based on any known requirement." This would indicate that experience may have convinced growers that, despite lack of experimental evidence, bee pollination is beneficial to this crop. The subject should be explored and the true pollination requirement of this important western forage determined.

Pollinators:
Evidence indicates that honey bees can be satisfactory pollinators of rose clover. Pollination Recommendations and Practices There are no recommendations for the use of pollinating insects on rose clover, although the reference by Bohart (1960*) indicates that growers believe they obtain some benefit from bee pollination.

LITERATURE CITED:
ARKLEY, R. J., HELPHINSTINE, W. N., and WILLIAMS, W. A.
1955. RANGELAND FORAGE ALMOST TREBLED BY SEEDING ROSE CLOVER AND USE OF SULFUR-BEARING FERTILIZERS. Calif. Agr. 9(8): 15-16.

BAILEY, E. T.
1966. ROSE CLOVER, DESCRIPTION, USE AND VARIETAL DIFFERENCES OF ROSE CLOVER IN WESTERN AUSTRALIA. West. Austral. Dept. Agr. Jour. (ser. 4) 7(4): 170-172,175.

HOLLAND, A. A.
1964. CLOVER ESTABLISHMENT IN NORTHERN CALIFORNIA. Calif. Agr. 18(7): 15.

LOVE, R. M., and SUMNER, D. C.
1952. ROSE CLOVER, A NEW WINTER LEGUME. Calif. Agr. Ext. Serv. Cir. 407,11 pp.

STRANG, J., and BROUE, P.
1958. ROSE CLOVER - A PROMISING SPECIES. Agr. Gaz. N.S. Wales 69(7): 368-369.

WILLIAMS, W. A., and LEONARD, O. A.
1959. EFFECT OF 2, 4-D ON THE GROWTH, SEED PRODUCTION, AND SEED VIABILITY OF ROSE CLOVER. Agron. Jour. 51: 383.

______LOVE, R. M., and BERRY, L. J.
1957. PRODUCTION OF RANGE CLOVERS. Calif. Agr. Expt. Sta. Cir. 458,19 pp.

STRAWBERRY CLOVER⁴¹Trifolium fragiferum L., family Leguminosae
Strawberry clover is grown to a limited degree as a pasture plant in moist and alkaline soils in the west coast States and the northern Great Plains (Graham 1941 *, Davies 1 962).
__________
⁴¹ See "Clovers, General."

Plant:
Strawberry clover is a perennial low-growing plant with creeping stems that root at the node to spread vegetatively as well as by seeds. The plant is difficult to distinguish from white clover when not in bloom. In maturity, the seeds are pressed closely to the ground making harvesting difficult. Tiver (1954) stated that strawberry clover in South Australia is a prolific seed producer, which yields up to 250 pounds of seed per acre.

Inflorescence:
The flower heads are round, pink to white, and resemble a strawberry, hence the name of the plant. The blooms appear earlier than those of white clover. There may be 35 to 60 florets per head. Only one seed forms in a floret. As the seeds mature, the head takes on the appearance of a balloon. The flowers are extremely attractive to bees for both nectar and pollen.

Pollination Requirements:
Johnson (1951) and Williams (1931) considered strawberry clover self-fertile. Hollowell (1939) also stated that the flowers are self- fertile, that crossing between flowers is not necessary, but that honey bees assist in the transfer of pollen to the stigmas. Davis and Young (1966) stated that most specimens from the Mediterranean area were completely self-sterile, but as the plant spread northward it was conditioned by its environment, probably lack of pollinating insects, to evolve into a self-fertile plant. Morley (1963) stated that the flowers are not self-pollinating and are largely self-incompatible. He stated, "It is difficult to understand how strawberry clover has been regarded as self- pollinating for so long. Seeds are expensive but shouldn't be if adequate honey bees are provided." He harvested only 0.25 seed per flower where bees were infrequent, but 0.70 per flower where bees were plentiful. Tiver (1954) considered honey bees important in increasing seed yields. Hollowell (1960) also noted that seed yields were increased if honey bee colonies were adjacent to the field. Todd (1957*) listed strawberry clover in the group of plants "Seed production increased by Bees."

Peterson et al. (1962) stated that common strawberry clover is self-fertile, but bees help to move the pollen to the stigma. 'Saline' strawberry clover, however, is self-sterile and will not set seed without cross-pollination. In this case, bee activity is essential for seed production.

Wright (1964) made a study of the pollination requirements of strawberry clover using material from Australia and New Zealand. He studied 66 clones and learned that most of them were self-incompatible but that some set a relatively high percentage of seed autogamously; however, they set more seed if they were cross-pollinated. He also found that self-pollinated plants were less vigorous. He considered strawberry clover a cross-pollinated species and found a high correlation between set of seeds from hand and bee pollination.

Pollinators:
Honey bees seem to be the primary pollinators.

Pollination Recommendations and Practices:
Morley (1963) spoke of providing adequate honey bees for high seed yields. Hollowell (1939) stated that placing colonies of honey bees adjacent to flowering fields is necessary, but he did not indicate the number of hives per acre needed.

LITERATURE CITED:
DAVIES, D. J. G.
1962. PALESTINE STRAWBERRY CLOVER A USEFUL SPECIES FOR LOW- LYING SOILS. New Zeal. Jour. Agr. 104(1): 79, 81-82.

DAVIS, W. E., and YOUNG, N. R.
1966. SELF-FERTILITY IN TRIFOLIUM FRAGIFERUM. Heredity 21: 615-624.

HOLLOWELL, E. A.
1939. STRAWBERRY CLOVER. U.S. Dept. Agr. Leaflet 176, 8 pp.

______ 1960. STRAWBERRY CLOVER: A LEGUME FOR THE WEST. U.S. Dept. Agr. Leaflet 464, 8 pp.

JOHNSON, I. J.
1951. (TABLE 9.1.) In Hughes, H. D., Heath, M. E., and Metcalf, D. S., Forages, 724 pp. Iowa State College Press, Ames.

MORLEY, F. H. W.
1963. THE MODE OF POLLINATION IN STRAWBERRY CLOVER (TRIFOLIUM FRAGIFERUM L.). Austral. Jour. Expt. Agr. and Anim. Husb. 3(8): 5-8.

PETERSON, M. L., STREET, J. E., and OSTERLI, V. P.
1962. SALINA STRAWBERRY CLOVER. Calif. Agr. Expt. Sta. and Agr. Ext. Serv. Leaflet 146.

TIVER, N. S.
1954. STRAWBERRY CLOVER. So. Austral. Jour. Agr. 57: 317-325.

WILLIAMS, R. D.
1931. FERTILITY OF VARIOUS HERBAGE LEGUMES. SELF-AND CROSS- FERTILITY AND FLOWERING HABITS OF CERTAIN HERBAGE GRASSES AND LEGUMES. Welsh Plant Breed. Sta., Univ. Col. of Wales Aberystwyth, ser. H., No. 12: 221-227.

WRIGHT, D. S. C.
1964. SELF- AND CROSS-FERTILITY IN STRAWBERRY CLOVER (TRIFOLIUM FRAGIFERUM L.). New Zeal. Jour. Agr. Res. 7(1): 32-36.

SUBTERRANEAN CLOVER⁴²Trifolium subterraneum L., family Leguminosae
__________
⁴² See "Clovers, General."

Plant:
Subterranean clover is a low, pliant, running, reseeding, annual legume, with short seedstalks that carry clusters of three to four small creamy to pinkish flowers. It will grow on soil with fertility so low white clover will not thrive. As a winter annual in both Southern and Northern Hemispheres, subterranean clover blooms and sets seed in spring or early summer. The seed is dormant until fall, at which time it germinates. The plant name is derived from the fruiting characteristics. The seed head is made up of a cluster of forked hairs or bristles turned back around the seed pods. The ripening seed head turns downward, and the forked hairs help to bury many of the heads in the soil, somewhat like a peanut, but about half of the heads remain above ground (Lancaster 1949, Smith 1948).

Inflorescence:
The flower is made up of three to seven, usually four, perfect, papilionate, usually white, florets. The ovary of each floret contains two ovules, but usually only one develops (Morley 1961). Yates (1957) found that above-ground seeds were poorer in quality than those that developed below the ground surface. Howell (1960) stated that this clover can be distinguished from other annual species in Western United States by its non-involucrate head of fertile flowers that become abruptly deflexed on their very short pedicel after they open. At that time, numerous sterile flowers develop, enclosing the fertile ones in the burrlike cluster.

Pollination Requirements:
Todd (1957*) placed subterranean clover in the group of plants considered to be largely self-pollinated. A reference by Knuth (1908*, p. 297) that the flowers "are capable of self-fertilization, though perhaps they do not always do this," leaves some doubt that maximum seed production results from selfing. Morley (1961) considered the species self-fertilizing but with occasional hybridization by outcrossing. How insects can get to the flowers, which are likely to be covered by the plant's leaves, is not explained. More study on this plant should be made to determine if it is benefited by visitation from pollinating insects.

Pollinators:
Morley (1961 ) stated that he had observed honey bees working the flowers, but only after fertilization would have taken place. However, he did not exclude them entirely as a cause of hybridization.

Pollination Recommendations and Practices:
None.

LITERATURE CITED:
LANCASTER, R. R.
1960. SUBTERRANEAN CLOVER (TRIFOLIUM SUBTERRANEUM) IN CALIFORNIA AND OREGON. West. Bot. Leaflet (San Francisco) 9(7): 114-115.

LANCASTER, R. R.
1949. CLOVERS FOR TEXAS PASTURES. Tex. Agr. Ext. Serv. B-168, 24 pp.

MORLEY, F. H. W.
1961. SUBTERRANEAN CLOVER. Adv. in Agron. 13: 57-123.

SMITH, E. G.
1948. SUBTERRANEAN CLOVER IN CANTERBURY PASTURES. New Zeal. Jour. Agr.76: 293-294.

YATES, J. J.
1957. SEED SETTING IN SUBTERRANEAN CLOVER (TRIFOLIUM SUBTERRANEUM L.). I. THE IMPORTANCE OF THE MICRO-ENVIRONMENT. Austral. Jour, Agr. Res. 8(5): 433-443.

SWEETCLOVER⁴⁵Melilotus spp., family Leguminosae
Two sweetclover species of importance are grown in the United States. They are sufficiently alike to be treated here as a single crop. The species, their common names, and cultivars are as follows:

[gfx] fix table:

Species Common name Cultivar M. officinalis (L.) Lam. Biennial yellow ÔAuraÕ, ÔGoldtopÕ, ÔMadridÕ. M. alba Desr. Biennial white ÔDentaÕ, ÔEvergreenÕ, ÔSpanishÕ, ÔWillametteÕ. M. alba annua1 Coe Annual white ÔEneraldÕ, ÔFlorannaÕ, ÔHubamÕ, ÔMelanaÕ. _________ l = subspecies.

Two other species, M. indica (L.) All. (yellow annual sour clover) and M. suaveolens Ledeb. (Daghastan sweetclover), are no longer important (Smith and Gorz 1965).

The production of sweetclover seed has decreased from 254,000 acres in 1955 to 65,000 in 1970, primarily because of the damage to the seedling plants by the sweetclover weevil (Sitona cylindricollis Fahraens). The leading States in seed production acreage included Minnesota (18,000), South Dakota (14,000), Kansas (7,000), Nebraska (6,500), North Dakota (6,000), Texas (5,000), Illinois (4,500), and Ohio (4,000 acres). Yields ranged from 100 to 280 lb/acre.

Sweetclover will grow wherever the soil has sufficient lime and more than 17 inches of rain is suitably distributed over the season or water is supplied by irrigation. It may therefore be found in the irrigated valleys of the high intermountain States, along the Canadian border, in Canada, in the hot irrigated valleys of the Southwest, or along the coast of the Gulf Coast States.

Sweetclover is grown for pasture, hay, seed, soil improvement, and erosion control. Beekeepers have encouraged its growth because of its attractiveness to bees and its value as a honey-producing plant.
__________
⁴⁵ See "Clovers, General."

Plant:

Sweetclover is an upright, drought-tolerant plant that may grow as tall as 10 feet but generally is 3 to 6 feet. It may have few or many fine branches, with shoots from buds near the crown and a branched, deep- penetrating, fleshy taproot. Its height, fragrant vanillalike odor, white or yellow flowering racemes, and trifoliate leaves are its identifying characteristics. In the South, the annual white cultivars are sometimes planted in the fall and turned under in the spring, or the seed is harvested in early summer. In the Northern States, they are planted in the spring, and the seed is harvested in the fall. The perennials are planted one year, then clipped or grazed, and allowed to set seed the following season.

Inflorescence:

The sweetclover inflorescence is a 1- to 4-inch-long slender spike or loose raceme of white or yellow florets (fig. 181). Each floret is about one-eighth of an inch long, and as many as 100 florets may occur on a single spike. The short corolla permits various short-tongued bees to reach the nectar. The spike grows from a node of the branch in the axil of the leaf. Within the floret, the stamens and pistil are enclosed in the keel. The weight of a bee on the keel will cause the staminal column to project upward and touch the bee but return to the original position after the pressure is released. This permits repeated effective pollination visits by bees. When the bee visits the flower, both pollen and nectar are collected, but the visits are primarily for the copious nectar secreted at the base of the corolla. The flowers are highly attractive to various species of bees, particularly honey bees. Holdaway and Burson (1960) stated that if sweetclover is in bloom bees will visit it in preference to other crops and may travel as much as 3 miles to do so. The flowers on plants deficient in soil moisture yield little nectar (Pankiw 1940).

[gfx] FIGURE 181. - Flowering stems of biennial white sweet clover.

Pollination Requirements:
The different species of sweetclover vary in their need for insect pollinators and are discussed separately.

Biennial yellow sweetclover is largely dependent upon pollinating insects for maximum seed production. Brink (1934) obtained only 5.1 percent set of seeds where flowers were not pollinated, 16.4 percent set when flowers were selfed, but 47.1 percent set when they were crossed. Kirk (1925) obtained only 2.6 pods per raceme on plants enclosed to exclude pollinating insects, but 63.9 per raceme on open-pollinated plants. Alex et al. (1952) using 'Madrid' cv. obtained only 11 pounds per acre in cages without bees, but 288 lb/acre on open plots. The following year they obtained 130 lb/acre in cages without bees, 248 lb/acre in cages with bees, and 396 lb/acre on open plots with about one-half colony per acre. Sandal and Johnson (1953) concluded that the incompatible characteristic is genetic and not mechanical. Todd (1957*) characterized M. officinalis as "normally cross-pollinated."

Biennial white sweetclover is greatly benefited by tripping and by cross-pollination between plants. Kirk (1925) obtained 34.9 pods per raceme on plants enclosed to prevent insect visitation but 66.4 pods per raceme on open-pollinated plants. Coe and Martin (1920) similarly obtained 29 and 66 percent set. Later Kirk and Stevenson (1931) stated that white sweetclover sets virtually no seeds when selfed. Shepperd (1927) also reported more than 100 percent increase in yield by honey bee pollination and that seed production was much higher within 120 rods of an apiary than beyond that distance. Pammel and King (1930*, pp. 363- 364) stated that the flowers were self-fertile but required bees to trip them. Pieters and Hollowell (1937), however, stated that the individual plants vary from self-sterile to self-fertile.

Munro (1950) obtained 22 times as much seed from open plants as from caged ones. Kirk and Davidson (1928) stated that plants could self if the pistil and stamens were the same length, but that few seeds were produced if the pistil were longer than the stamens. Hartwig (1942) showed that plants from selfed seeds are less likely to produce seed than plants from cross-pollinated seed. Thus, a seed producer would be wise to plant seeds from fields that received maximum cross-pollination.

Alex et al. (1952) obtained only 33 lb/acre of seed from 'Evergreen' caged to exclude bees, 116 lb/acre from similar cages with honey bees present, and 146 lb/acre from adjacent open plots provided with about one colony of honey bees per acre. Holdaway et al. (1957) obtained 6 lb/acre without bees in contrast to 1,078 lb/acre with bee pollination. In another test, they obtained only 11 lb/acre from plots caged to exclude bees, but 288 lb/acre from open plots. This showed the need for bee pollination on biennial white clover indicated by Garver et al. (1943) and Todd (1957*).

Annual white sweetclover falls in the same pollination category as biennial white. Weaver et al. (1953) obtained only 16 lb/acre from 'Hubam' cv. plots caged to exclude bees, 157 lb/acre from similar plots enclosing honey bees, and 130 lb/acre from open plots in a 200-acre area supplied with 55 colonies of bees. The plants were admittedly stunted from a severe drought. Weaver et al. (1953) concluded that 'Hubam' clover supplied with an adequate number of bees will yield 10 times as much seed as clover from which bees are excluded.

Yellow annual sourclover or sour sweetclover is seldom used in the United States. It is visited by bees and is commonly reported as a honey plant but is not nearly as important as the other sweetclovers. It is considered to be a largely self-pollinated plant (Lancaster 1949, Smith 1927, Todd 1957*) although little data support this assumption.

The effective time period for pollination of all sweetclover flowers has not been determined. Weaver et al. (1953) stated that blossoms wither quickly after they are pollinated, but those not pollinated remain open for days.

Pollinators:
Although numerous pollinating insects visit the blossoms of sweetclover, none are nearly as important on this crop as honey bees (fig. 182). Few if any plants are more attractive to honey bees than sweetclover. For commercial pollination of this crop, honey bees are by far the most effective and practical agents.

[gfx] FIGURE 182. - Honey bee collecting nectar from sweet clover, a plant highly attractive to bees and a major source of honey.

Pollination Recommendations and Practices:
Jaycox (1971), Munro (1950), and Wheeler (1950) suggested that one colony of honey bees per acre of sweetclover was adequate. Todd (1957*) recommended one to two colonies per acre, Haws and Holdaway (1957) recommended two colonies per acre, although their data showed that seed yields were progressively increased to 10 colonies per acre. Pedersen et al. (1961) recommended two or more colonies per acre. Smith (1960) suggested two to three colonies per acre, the colonies within easy flight range of the field. The extremes were probably given in a statement (Anonymous 1944), made without apparent verification, that one colony per acre was generally recommended, but 10 colonies per acre was nearer th