Chap. VII. POLYGAMOUS PLANTS. 281 



other forms, and has somewhat smaller pollen-grains 

 which have less fertilising power than those of the cor- 

 responding stamens in the other two forms ; but whether 

 the larger number of seeds is the indirect cause of the 

 diminished power of the pollen, or vice versa, I know 

 not. As soon as the anthers in a certain number of 

 individuals became reduced in size in the manner 

 just suggested or from any other cause, the other in- 

 dividuals would have to produce a larger supply of pol- 

 len; and such increased development would tend to 

 reduce the female organs through the law of compen- 

 sation, so as ultimately to leave them in a rudimen- 

 tary condition; and the species would then become 

 dioecious. 



Instead of the first change occurring in the female 

 organs we may suppose that the male ones first varied, 

 so that some individuals produced a larger supply of 

 pollen. This would be beneficial under certain cir- 

 cumstances, such as a change in the nature of the in- 

 sects which visited the flowers, or in their becoming more 

 anemophilous, for such plants require an enormous quan- 

 tity of pollen. The increased action of the male organs 

 would tend to affect through compensation the female 

 organs of the same flower ; and the final result would be 

 that the species would consist of males and hermaphro- 

 dites. But it is of no use considering this case and 

 other analogous ones, for, as stated in the Introduction, 

 the co-existence of male and hermaphrodite plants is ex- 

 cessively rare. 



It is no valid objection to the foregoing views that 

 changes of such a nature would be effected with ex- 

 treme slowness, for we shall presently see good reason 

 to believe that various hermaphrodite plants have be- 

 come or are becoming dioecious by many and excessively 

 small steps. In the case of polygamous species which 







