284: DIOECIOUS AND CHAP. VII. 



Introduction, in which some of the individuals of both 

 monoecious and hermaphrodite plants are proterand- 

 rous, others being proterogynous, their conversion into 

 a dioecious condition would probably be much facili- 

 tated, as they already consist of two bodies of individ- 

 uals, differing to a certain extent in their reproductive 

 functions. 



Dimorphic heterostyled plants offer still more 

 strongly marked facilities for becoming dioecious; for 

 they likewise consist of two bodies of individuals in 

 approximately equal numbers, and, what probably is 

 more important, both the male and female organs 

 differ in the two forms, not only in structure but in 

 function, in nearly the same manner as do the repro- 

 ductive organs of two distinct species belonging to 

 the same genus. Now, if two species are subjected to 

 changed conditions, though of the same nature, it is 

 notorious that they are often affected very differently; 

 therefore the male organs, for instance, in one form of 

 a heterostyled plant might be affected by those un- 

 known causes which induce abortion, differently from 

 the homologous but functionally different organs in 

 the other form; and so conversely with the female or- 

 gans. Thus the great difficulty before alluded to is much 

 lessened in understanding how any cause whatever could 

 lead to the simultaneous reduction and ultimate sup- 

 pression of the male organs in half the individuals of 

 a species, and of the female organs in the other half, 

 whilst all were subjected to exactly the same conditions 

 of life. 



That such reduction or suppression has occurred 

 in some heterostyled plants is almost certain. The 

 Rubiacea? contained more heterostyled genera than any 

 other family, and from their wide distribution we may 

 infer that many of them became heterostyled at a re- 



