418 REVIEW AND CONCLUSION 



we have come to these two great classes, and has enabled 

 us to separate what, from the point of view of rela- 

 tionship, are the more, from the less important 

 characters ; and this is the aim of all scientific classifi- 

 cation. It is as if we were examining the branch 

 system of a tree whose stem bifurcates close to the 

 ground and then divides into many branches which 

 end in twigs representing the different species. And 

 just as every twig has arisen, and usually with several 

 others, by lateral development of a twig of the previous 

 year, so probably is every species more closely allied 

 to some than to others of the same genus, and derived 

 with them from some pre-existing species. Into the 

 commonly accepted view of the process by which 

 this has been brought about we cannot enter here ; it 

 is closely connected with the extraordinary adaptation 

 of every species to its environment which has been 

 repeatedly pointed out, but has nothing to do with the 

 reaction of the individual to the influences of its 

 immediate environment, and applies in equal degree to 

 plants and animals. 



GENERAL 



In the introductory chapter plants were referred to 

 as making up with animals the animate portion of 

 our world, differing from the inanimate creation in the 

 ability to feed, grow, and reproduce each its own kind. 

 And though they differ in many respects there are 

 other points of resemblance between the two sections. 



Both animals and plants respire, that is give out 

 carbon dioxide as a result of those internal changes 

 in the living substance itself on which life depends. 



