350 THE SURVIVAL OF THE UNLIKE, [xxi. 



This fact — the impotency of wrtnin pLints with 

 themselves — is itself of immense praetical importanee, 

 but we are anxious to know if such characters are 

 likely to increase amonj? cultivated plants, and if the 

 futui-e holds more pci-plexity than the present. We 

 have found that as stiiiggle for existence increased 

 and organisms became more complex, animals could 

 not afford to be hermai)hrodite or bisexual, for all 

 the surplus energy was needed for the development of 

 a single sex. Among plants, this separation of the 

 sexes has proceeded slowly, perhaps because of their 

 exceedingly constructive or vegetative character, which 

 supplies sufficient nutriment to maintain both sexes 

 in greater or less perfection. But the fvirther we 

 develop fruits, the greater is the energy required in 

 the production of that fruit, and the greater, it would 

 seem, must be the tendency toward the suppression 

 of one sex in given individuals, or toward the evolu- 

 tion of unisexual individuals. Now, it is highly 

 probable that one of the first steps in the separation 

 of the sexes is a differentiation in their mutual rela- 

 tionships, whether a difference in time of maturing 

 of the sex-elements or in the comparative intimacy 

 with which they react upon encli otlier. If these 

 speculations are well founded, it leads us to the con- 

 clusion that this impotency among cultivated plants 

 is the beginning of a potential tendency towards uni- 

 sexuality, and that such impotency is likely to 

 increase, rather than diminish, with the grentcr 

 amelioration of the species. The reader may think 

 this conclusion counter to the observed facts in the 

 vegetable kingdom, where unisexuality does not appear 

 to be associated with the progressive development of 



