Reproduction 359 



As a matter of fact, there are several grades of self- 

 fertilization ; thus fertilization as a result of pollinating 

 the stigma with pollen from the same blossom, from a 

 different blossom upon the same plant, or from another 

 plant derived by bud or scion propagation from the same 

 " parent ' stock. In much the same way cross-fertiliza- 

 tion is a broad term, applying when the gametes are de- 

 rived from any two individuals (grown from seed) within 

 the species; that is, whether the crossing is between indi- 

 viduals from pure lines, from merely mixed seeds, or from 

 distinctly different strains or races. 



When reference is made merely to the dusting with 

 pollen, the terms self and cross pollination should be 

 employed, but many authors writing popularly fail to 

 make these distinctions. 



209. Cross-fertilization apparently the rule. - - Cross- 

 fertilization is a phenomenon of common occurrence with a 

 considerable number of ecologically well-established native 

 species of plants, and vigorous cultivated varieties as 

 well. It is evidently effective, but it is by no means uni- 

 versal among seed-plants. If we accept the analysis 

 which has thus far been made, it is, however, far the more 

 common method among flowering plants. Cross-fertiliza- 

 tion is, of course, dependent upon cross-pollination, and 

 both are commonly associated with the remarkable 

 developments in form, color, and other characteristics of 

 numerous familiar flowers to which popular attention has 

 been so much attracted. Nevertheless, it should not be 

 understood that these striking peculiarities of floral 

 structures are in strict correlation with cross-pollination. 

 Dates, mulberries, hops, and hemp are invariably cross- 



