ii6 MENDELISM chap. 



If we turn from animals to plants we find a more 

 complicated state of affairs. Generally speaking, the 

 higher plants are hermaphrodite, both ovules and 

 pollen grains occurring on the same flower. Some 

 plants, however, like most animals, are of separate 

 sexes, a single plant bearing only male or female 

 flowers. In other plants the separate flowers are 

 either male or female, though both are borne on the 

 same individual. In others, again, the conditions are 

 even more complex, for the same plant may bear 

 flowers of three kinds, viz. male, female, and herma- 

 phrodite. Or it may be that these three forms 

 occur in the same species but in different individuals 

 — female and hermaphrodites in one species ; males, 

 females, and hermaphrodites in another. One case, 

 however, must be mentioned as it suggests a possi- 

 bility which we have not hitherto encountered. In 

 the common English bryony {Bryonia dioica) the 

 sexes are separate, some plants having only male 

 and others only female flowers. In another Euro- 

 pean species, B. alba, both male and female flowers 

 occur on the same plant. Correns crossed these 

 two species reciprocally, and also fertilised B. dioica 

 by its own male with the following results : — 



dioica ? x dioica $ gave ? ? and $ $ 



„ X alba $ „ ? 9 only 



alba ? X dioica (? „ ? $ and $ $. 



The point of chief interest lies in the striking differ- 

 ence shown by the reciprocal crosses between dioica 

 and alba. Males appear when alba is used as the 

 female parent but not when the female dioica is 

 crossed by male alba. It is possible to suggest 



