104 



ELEMKXTAKY STUDIES IN INSECT LIFE 



the orchard to insure' the visitation of the blossoms, but 

 the different varieties of each fruit should be placed 

 promiscuously throughout the orchard in order to facil- 

 itate the work of cross-fertilization. 



Plants whose Flowers are so Constructed as to Prevent 

 Self-fertilization. A papilionaceous flower is an exam- 

 ple of a blossom so constructed as tn prevent the falling 

 of the pollen upon the stigma of its own pistil. The 

 alfalfa blossom is an example of this class. Its structure 

 and component parts are illustrated in Figure 85. It 

 will be seen that the stigma of the ovary is higher than 

 the pollen-producing anthers, so that the grains of pollen 

 may all drop to the base of the flower and the ovule go 

 unfertilized; such being the case, no seed would be 

 formed. Small forms resembling seed might be found 

 within the ovary at maturity, but these, not being fer- 

 tilized, would not germinate. 



From the shape and size of the alfalfa blossom, it is 

 not probable that cross-fertilization could be safely 

 accomplished by means of currents of air. 



It becomes evident, then, that outside agencies must 

 be called upon, and the plant must provide for these 

 agencies. The agents in this case we find to be insects, 

 and the reward offered by the plant for favors rendered 

 is a sweet drop of nectar; that is, the flower in an en- 

 ticing way places a tempting sip of nectar in such a 

 position that when the insect has favored the flower with 

 a few grains of pollen unconsciously brought from an 

 adjoining flower and just as unconsciously left, the cov- 

 eted sip may be enjoyed. It is evident, however, that 

 the first flower visited will not be cross-fertilized. 



The location of the coveted nectar at the base of 



