38 THEORY OF ORGANIC EVOLUTION. 



remain united with each other, multicellular plants 

 arise from unicellular. The same transformation 

 of the reproductive cells into non-separable tissue 

 cells is repeated several times in multicellular plants 

 and serves to enlarge the individual. There is 

 manifested in this phylogenetic process the ten- 

 dency of the plant to combine in the higher stages 

 into one complex whole those parts which in the 

 lower stages tend to be independent. A similar 

 unifying tendency is revealed also in those plant 

 members which have arisen by differentiation and 

 represent a system only by their being connected at 

 certain points. These combine in the higher stages 

 and form ultimately continuous tissues. 



Law of Phylogenetic Complication or A nipliation, 

 Differentiation and Reduction. The cells, and, in 

 general, the parts of plants which lie near each other 

 in space or follow upon each other in time, are 

 always alike in the lower stages. By differentia- 

 tion they become unlike, so that the sum of 

 the functions which at first fall to the lot of 

 all parts without distinction now is shared among 

 the individual parts. By this means each part can 

 perform its own special function so much the better. 

 Differentiation is repeated in the course of the phy- 

 logeny, since at first all parts of an ontogeny diverge 

 into two or more parts, then the parts of these parts 

 divide again, etc. Along with this process of divi- 

 sion another process is always active, which, as it 



