THE EVOLUTION PROCESS 235 



ogy of human selection upon domestic ani- 

 mals and cultivated plants, and reasoning 

 from the accumulation of their varietal 

 differences up to what seem to correspond to 

 species or sometimes even genera in Nature, 

 and thence arguing on Lyell's uniformitarian 

 principle, for the analogous cumulative nat- 

 ural selection through geological time, of the 

 characters of larger groups, genera, orders, 

 classes and the rest. We have simply now 

 to group our types of variation, and to con- 

 sider them from the standpoint of general 

 physiology as far as we know it, and inde- 

 pendently of these fascinating hypotheses of 

 agriculture and geology. 



VEGETATION AND REPRODUCTION, AND 

 THEIR ANTITHESIS. The largest view of 

 physiology, one peculiarly obvious to the 

 botanist, from the vivid distinctness of 

 flowers and foliage, but denied by none for 

 animals and man as well, is that which treats 

 the functions of living beings as of two main 

 kinds; grouping on the one side respiration, 

 irritability, and all the other activities of the 

 individual in its self-maintaining life, and 

 then setting over against the whole of these 

 the great function of the species-maintaining 

 life, reproduction. Weismann's main work 

 has been to emphasize this distinction, espe- 

 cially from the side of the intimate morphol- 



