RED-CLOVER SEED PRODUCTION. 9 



100 per cent of infertile ovules. With such plants the presence of 

 bees is not a matter of importance, for the ovules have no reproduc- 

 tive cells; hence there can be no fertilization and no production of 

 seed. During the second crop, when the season is generally dry and 

 favorable for seed setting, there is some infertility, ranging from a 

 low percentage or none in some plants to a high percentage in others. 

 It is very probable that this infertility of ovules is to a greater or less 

 degree a hereditary character and that the production of a high- 

 yielding strain will consist, among other features, in selecting those 

 plants with the least tendency toward infertility. 



POLLEN OF RED CLOVER. 



The pollen grains of red clover are almost globular when turgid, 

 with a little flattening at the germ pores. When measured in a 

 25 per cent cane-sugar solution the pollen grams have an average 

 size of 44.5 by 43 n (fig. 2, E). The grains are not fully turgid when 

 shed from the anthers and one diameter in each is shortened and 

 the other diameter lengthened by an infolding of the wall. In this 

 condition Martin (25) found the average dimensions of 100 pollen 

 grains to be 26 by 48 p., while Miss Clark (30) found the average size 

 of 1,024 pollen grains to be 31.7 by 56.29 p. 



When dropped in water the pollen grains take it up very rapidly 

 and burst almost instantly. On account of this feature of the pollen 

 there can be little effective pollination when the flowers are wet. 

 Pollination at night or in the morning when the flowers are wet 

 with dew is not likely to be effective. 



Germination of the pollen of red clover was found by Martin (25) 

 to depend upon a proper water supply. Good artificial germination 

 can be secured on parchment paper or animal membranes which are 

 just moist enough to permit the pollen to absorb the requisite amount 

 of water for germination. Germination takes place within a limited 

 range of variation in the water supply, and it is only by trials of 

 wetting and drying that the proper moisture content of the mem- 

 branes may be secured. Under proper conditions of moisture and 

 temperature, germination takes place usually in 8 to 10 minutes. 



FUNCTION OF THE STIGMAS OF RED-CLOVER FLOWERS. 



Micro chemical, tests of the stigmas of red-clover flowers show 

 no sugars or starches present. An oily emulsion, however, does 

 occur in the papillae. Crushed stigmas placed on animal membranes 

 had no apparent effect on the germination of the pollen or on the 

 directions of the tubes. 



When pollen is deposited on the stigmas it lodges between the 

 papillae, takes up water, and soon becomes turgid, but the water 

 supply is so regulated by the stigmas that no bursting occurs. It 

 2990°— Bull. 289—15 2 



