Chap. VII. POLYGAMOUS PLANTS. 281 



number of seeds than the other forms, and has some- 

 what smaller pollen-grains which have less fertilising 

 power than those of the corresponding 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 viae versa, I know not. As soon 

 as the anthers in a certain number of individuals be- 

 came reduced in size in the manner just suggested or 

 from any other cause, the other individuals would have 

 to produce a larger supply of pollen; and such in- 

 creased development would tend to reduce the female 

 organs through the law of compensation, so as ulti- 

 mately to leave them in a rudimentary 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 

 insects which visited the flowers, or in their be- 

 coming more anemophilous, for such plants require an 

 enormous quantity of pollen. The increased action of 

 the male organs would tend to affect through compen- 

 sation the female organs of the same flower ; and the 

 final result would be that the species would consist of 

 males and hermaphrodites. But it is of no use con- 

 sidering this case and other analogous ones, for, as 

 stated in the Introduction, the co-existence of male 

 and hermaphrodite plants is excessively 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 

 become or are becoming dioecious by many and ex- 

 cessively small steps. In the case of polygamous 



