ALFALFA 



349 



Numerous investigators have studied the process and 

 have experimented in various ways with the flowers. 

 These researches have shown that only in very rare cases 

 will an alfalfa flower set seed without being tripped ; 

 that self-tripping takes place under certain conditions; 

 that artificial tripping with self-pollination is hardly 

 as efficacious as cross-pollination; that honey-bees are 

 usually unable to trip the flowers, bumble bees and other 

 large bees being the most efficient insects. BurkilPs 

 contention that the stigma must be ruptured or irritated 

 by striking -the standard or an insect does not hold true 

 under American conditions. Cross-pollination results in 

 the production of about 30 per cent more seeds to the 

 pod than does self-pollination. It has not been definitely 

 shown, however, that cross-pollinated seeds possess any 

 superiority. 



Under Western conditions, it is probable that more 

 flowers are self -tripped than are tripped by insects, but 

 more quantitative data on this point are needed. 



414. Seeds. Alfalfa 

 seed may be adulterated 

 with that of trefoil, sweet 

 clover or bur clover. All 

 of these resemble alfalfa 

 seeds closely. The sweet 

 clover can be detected 

 easily by crushing a few 

 seeds when the character- 

 istic vanilla-like odor of 

 the sweet clover will re- 

 veal its presence. A very 



small amount of sweet clover seed, up to 5 per cent, 

 is sometimes present in American seed as an impurity, 



FIG. 36. Alfalfa seeds : a, indi- 

 vidual seeds, showing variation in 

 form ; b, edge view of a seed, show- 

 ing the scar ; c, natural size of seeds. 



