22 INTRODUCTION 



which the pollen gets from the anther to the stigma 

 is called pollination. In case the pollen comes 

 from the same flower it is said to be a case of 

 self-pollination; in case it comes from another 

 flower, perhaps upon the same plant but preferably 

 upon another plant of the same species, it is said 

 to be a case of cross-pollination. In general we 

 know that flowers exist chiefly in order that they 

 may attract insects to bring about cross-pollina- 

 tion and the consequent cross-fertilization that 

 results. As Darwin said, " nature abhors per- 

 petual self-fertilization." 



Cross-pollination may take place through the 

 agency of winds, of birds like the humming-bird, 

 and of insects. The great majority of our com- 

 mon flowers have the pollen carried by insects. 

 Such flowers are said to be entomophilous or 

 insect-loving flowers, while those which depend 

 upon the wind for the carrying of their pollen are 

 said to be anemophilous or wind-loving flowers. 



It not infrequently happens that the nectar in 

 the flower is protected from the visits of ants and 

 other wingless insects, which would not make 

 effective pollen carriers, by some such special 

 device as a fringe of hairs within the corolla or 

 sets of viscid hairs upon the outside of the flower. 



From the point of view of the life relations of 

 the plant three questions may be asked in regard 

 to any flower, namely: 



