FERTILIZATION. 83 



of plants to active external agencies. The 

 science slept, however, until that critical 

 student of nature, Darwin, made investiga- 

 tions and published his celebrated work 

 upon the " Fertilization of Orchids," in 1862. 

 Since that event a rich special literature has 

 sprung up, an important part of which has 

 been contributed by Darwin himself. 



Two terms which have now come into 

 general use are dose -fertilization^ or self- 

 fertilization^ and cross-fertilization. Close- 

 fertilization refers to the impregnation of a 

 stigma by pollen from its own flower, while 

 cross-fertilization denotes the impregnation 

 of a stigma by pollen from a different flower. 

 It is now known that close-fertilization is 

 not the common occurrence in the vegetable 

 kingdom, and that in nearly all species cross- 

 fertilization takes place to a greater or less 

 extent. " Nature seems to have wished that 

 no flower should be fertilized by its own pol- 

 len," said Sprengel, a statement not strictly 

 true, for there are some flowers in which 

 cross-fertilization cannot take place. Dar- 

 win's statement is better: "Nature abhors 

 perpetual self-fertilization." 



It is evident that cross-fertilization must 

 take place in dioecious and monoecious plants. 



