262 CONCLUDING EEMAEKS Chap. VI. 



thus varied, it would never have been rendered hetero- 

 styled, as this state would then have been superfluoug. 

 But the parent-species of our several existing hetero- 

 styled plants may have been, and probably were (judg- 

 ing from their present constitution) in some degree 

 self-sterile ; and this would have made regular cross- 

 fertilisation still more desirable. 



Now let us take a highly varying species with most 

 or all of the anthers exserted in some individuals, and 

 in others seated low down in the corolla ; with the 

 stigma also varying in position in like manner. Insects 

 which visited such flowers would have different parts 

 of their bodies dusted with pollen, and it would be a 

 mere chance whether this were left on the stigma of 

 the next flower which was visited. If all the anthers 

 could have been placed on the same level in all the 

 plants, then abundant pollen would have adhered to 

 the same part of the body of the insects which fre- 

 quented the flowers, and would afterwards have been 

 deposited without loss on the stigma, if it likewise 

 stood on the same unvarying level in all the flowers. 

 But as the stamens and pistils are supposed to have 

 already varied much in length and to be still varying, 

 it might well happen that they could be reduced much 

 more easily through natural selection into two sets of 

 different lengths in different individuals, than all to 

 the same length and level in all the individuals. We 

 know from innumerable instances, in which the two 

 sexes and the young of the same species differ, that 

 there is no difficulty in two or more sets of individuals 

 being formed which inherit different characters. In 

 our particular case the law of compensation or balance* 

 ment (which is admitted by many botanists) would 

 tend to cause the pistil to be reduced in those indi- 



