No. 4.] CROSSING OF PLANTS. 23 



tion, at least, is due to external circumstances. We are 

 now looking for the cause of variation along some of the 

 lines of evolution ; and we are wondering if the varied sur- 

 roundings, or, as Darwin put it, the "changed conditions of 

 life," may not actually induce variability. This conclusion 

 would seem to follow to some extent, from the fact of the 

 severe and universal struggle in nature whereby plants are 

 constantly forced into new and strange conditions. But 

 there is undoubtedly much variation which has sprung from 

 more remote causes, one of which it is my purpose to dis- 

 cuss here. 



In the lowest animals and plants the species multiplies by 

 means of simple division or by budding. One individual, 

 of itself, becomes two, and the two are therefore re-casts of 

 the one. But, as organisms multiplied and conditions 

 became more complex, that is, as struggle increased, there 

 came a differentiation in the parts of the individual, so that 

 one cell or one cluster of cells performed one labor and other 

 cells performed other labor ; and this tendency resulted in 

 the development of organs. Simple division, therefore, 

 could no longer reproduce the whole complex individual ; 

 and, as all organs are necessary to the existence of life, the 

 organism dies if it is divided. Along with this speciali- 

 zation came the differentiation into sex ; and sex clearly 

 has two offices : to hand over, by some mysterious process, 

 the complex organization of the parent to the offspring, 

 and also to unite the essential characters or tendencies of 

 two beings into one. The second office is manifestly 

 the greater; for, as it unites two organizations into one, 

 it insures that the offspring is somewhat unlike either 

 parent, and is therefore better fitted to seize upon any place 

 or condition new to its kind. And, as the generations 

 increase, the tendency to variation in the offspring must be 

 constantly greater, because the impressions of a greater 

 number of ancestors are transmitted to it. I have said that 

 this office of sex to induce variation is more important than 

 the mere fact of reproduction of a complex organization ; 

 for it must be borne in mind that the complexity of organi- 

 zation is itself a variation, made necessary by the increasing 

 struggle for existence. 



