THE EVOLUTION OF LIFE 



the innumerable elementary organs in the cell-monarchy 

 of the animal body are much more intricate, yet at the 

 same time much more intelligible, than those of the 

 cell-republic of the higher plant-body. Thus the phylog- 

 eny of the plants encounters much greater dithculties 

 than that of the animals; the embryology of the former 

 says much less in detail than that of the latter. We 

 can understand, therefore, why the biogenetic law is not 

 so generally recognized by botanists as by zoologists. 

 Paleontology, which provides such valuable fossil ma- 

 terial for many groups of the animal kingdom that we 

 can more or less correctly draw up their ancestral tree 

 on the strength of this, gives us very little for most 

 groups of the plant kingdom. On the other hand, the 

 large and sharply demarcated plant-cell, with its va- 

 rious organella, is much more valuable in connection 

 with many problems than the tiny animal-cell. For 

 many physiological purposes, in fact, the higher plant 

 body is more accessible to exact physical and chemical 

 research than the higher animal body. The antithesis 

 is less in the kingdom of the protists, as the difference 

 between animal and vegetal life is mostly conhned to 

 difference of metabolism, and finally disappears alto- 

 gether in the province of the unicellular forms of life. 

 Hence, for a clear and impartial treatment of the great 

 problems of biology, and especially of phylogeny, it is 

 imperative to have a knowledge of both zoological and 

 botanical investigation. The two great founders of the 

 theory of descent — Lamarck and Darwin — were able to 

 penetrate so deeply into the mysteries of organic life 

 and its development because they had extensive attain- 

 ments both in botany and zoology. 



Of the various tendencies that have recently made 

 their appearance among zoologists and botanists in the 

 discussion of the theory of descent, we frequently fiml 

 Neo-Lamarckism and Neo-Darwinism distinguished as 



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