LEGUMES IN GENERAL 243 



and these in turn depress the ' keel ' petals ; the stamens, 

 style, and stigma are by this movement forced out at the 

 apex of the ' keel,' and the pollen is brought into contact 

 with the underneath part of the insect's body. The in- 

 sect visiting other flowers brings the pollen on its body into 

 contact with the stigma of the flower, which, on account 

 of its length and position, is generally forced out first from 

 the apex of the ' keel ' ; cross pollination is thus effected. 



" Some plants, such as the garden and field pea, sweet 

 pea, the vetches and trefoil, while undoubtedly possessing 

 flowers specially adapted for insect pollination, are ca- 

 pable of self-pollination, and are fertile and able to produce 

 seeds when insects are excluded. Others, such as the 

 red, white, and crimson clovers and the broad bean, are 

 more or less sterile when insects are prevented from 

 visiting the flowers." 



243. Much controversy has arisen regarding the im- 

 portance of insects in the pollination of the clovers, and 

 their influence on the seed crop. Several experiment 

 stations have conducted tests to determine whether or 

 not insects are responsible for the clover seed crop. The 

 test consists in protecting small areas of clover by frames 

 covered with wire screen. In some of the cages are 

 placed insects of various kinds, while in others no insects 

 are permitted to visit the flowers. The report on the 

 following page of a test conducted on red clover by the 

 North Dakota Station shows the importance of insects. 



The results show that the bumble-bees were responsible 

 for about 95 per cent of the seed formed in the protected 

 cages. While heads selected growing in the fields showed 

 a larger percentage of seeds per head, it was pointed out 

 that the bumble-bees in the cages, being confined, were 

 not under normal conditions : 



