POLLINATION 



109 



no sexual plants which can constantly reproduce them- 

 selves by self-fertilization alone; cross-pollination is 

 possible in all ; in most cases self-fertilization is pre- 

 vented by special adaptations, or is impossible, or 

 at least not advantageous, while cross-fertilization 

 alone can occur, does actually occur, or has good 

 results". On the results of investigations by Darwin 

 and others, Hermann Miiller has formulated the fol- 

 lowing proposition: "Whenever progeny resulting 

 from crossing comes into serious conflict with the 

 offspring resulting from self-fertilization, the former 

 is victorious. Only where there is no such struggle 

 for existence can self-fertilization often prove satis- 

 factory for many generations." Sprengel, who to- 

 gether with Kohlreuter may be regarded as the founder 

 of the study of flower-pollination, has added the fol- 

 lowing remark about pollination: "As very many 

 flowers are of separate sexes, and probably quite as 

 many of the hermaphrodite ones are dichogamous, it 

 seems that Nature is unwilling that any flower should 

 be fertilized by its own pollen". 



Examples may now be cited to illustrate the difl"erent 

 groups of flowers referred to above. The nature of 

 their pollination will be discussed in detail in another 

 chapter. 



First, unisexual flowers. Shasha or Cucumber, 

 tarmuz or Water-melon, belati-kumrha or Gourd, in- 

 fact all plants belonging to the Natural Order Cuciirbi- 

 tacece; most plants of the Natural Order Euphorbi- 

 acece, such as lal-bharenda, rerhi or Castor-oil plant, 

 pituli {Trewia nudifiora); most Palms, such as tal- 

 palm, khejur or Date-palm; several Graminacece, 

 such as bhutta or Indian Corn, are well known 

 examples of plants with unisexual flowers. Gymno- 

 spermia as a class are all unisexual. 



