THE MOVEMENTS AND HABITS OF PLANTS. 13 



which can not themselTes produce offspring ? The an- 

 swer lies, as I can hardly doubt, in the great good which 

 is derived from the fusion of two somewhat differentiated 

 individuals ; and with the exception of the lowest organ- 

 isms this is possible only by means of the sexual elements, 

 these consisting of cells separated from the body, con- 

 taining the germs of every part, and capable of being 

 fused completely together. 



It has been shown in the present volume that the 

 offspring from the union of two distinct individuals, 

 especially if their progenitors have been subjected to very 

 different conditions, have an immense advantage in height, 

 weight, constitutional vigor and fertility over the self- 

 fertilized offspring from one of the same parents. And 

 this fact is amply sufficient to account for the develop- 

 ment of the sexual elements, that is, for the genesis of 

 the two sexes. 



It is a different question why the two sexes are some- 

 times combined in the same individual, and are sometimes 

 separated. As with many of the lowest plants and ani- 

 mals the conjugation of two individuals, which are either 

 quite similar or in some degree different is a common 

 phenomenon, it seems probable, as remarked in the last 

 chapter, that the sexes were primordially separate. The 

 individual which receives the contents of the other, may 

 be called the female ; and the other, which is often smaller 

 and more locomotive, may be called the male ; though 

 these sexual names ought hardly to be applied as long as 

 the whole contents of the two forms are blended into 

 one. The object gained by the two sexes becoming united 

 in the same hermaphrodite form probably is to allow of 

 occasional or frequent self-fertilization, so as to insure 

 the propagation of the species, more especially in the 

 case of organisms affixed for life to the same spot. 



