RED CLOVER 387 



458. Pollination and fecundation. The flowers of 

 red clover are especially adapted to being cross-pollinated 

 by insects, especially bumble bees. 



Miiller records 39 species of insects that visit red clover 

 flowers in Germany. One species of bumble bee secures 

 the honey by biting through the base of the corolla. For 

 Iowa, Pammel records 14 species, 8 of them being bumble 

 bees. In Illinois, Robertson observed 20 species, five 

 of them being bumble bees. 



Plants screened from flying insects failed to set any 

 seeds in the experiments conducted by Darwin in Eng- 

 land, and this has been the common result secured by later 

 experimenters. Some investigators have, however, found 

 a few seeds produced by screened plants. 



Frandsen in Sweden has recently made extensive studies 

 regarding the matter. In 1910 out of numerous bagged 

 and undisturbed flowers he secured no seed; when arti- 

 ficially self -pollinated, 0.1 per cent of the flowers set seed ; 

 when artificially pollinated by another flower of the same 

 plant, 0.8 per cent ; when artificially cross-pollinated, 

 46.1 per cent. In 1911 in similar experiments the per- 

 centage of seeds to flowers by the three methods was, 

 respectively, per cent, 0.1 per cent, '0.4 per cent and 

 42.3 per cent. 



Waldron at Dickinson, North Dakota, found that 

 53.6 per cent of the heads produced seeds in the open and 

 but 9 per cent when screened. When butterflies were 

 placed in netting tents over red clover, only 2.4 per cent 

 of the heads set seed, but when bumble bees were thus 

 placed, 45.7 per cent of the heads produced seeds. 



459. Seed-production. Medium red clover seed is 

 mainly produced in those regions where a crop of seed 

 can be procured after one of hay has been harvested. In 



