TJie Biochronic Equation. 673 



extraordinary richness of its forms, from a relatively 

 small number of elementary units, for almost evcr\' indi- 

 vidual character is found in numerous sj)ecies, and it is 

 to their different grouping and their combination with 

 the rarer factors that the extraordinary diversity of liv- 

 ing forms is due.^ 



As we can easily see, this view effects a considerable 

 simplification of the problem. ^lany authors have ex- 

 pressed their agreement with it, and only last year 

 Schneider stated his opinion clearly enough, when he 

 said that the number of histological characters is by no 

 means a very large one.^ 



The question is, however, how many elementary char- 

 acters an angiosperm or a higher animal posses,ses, on 

 the average. In the former case I have attempted to 

 draw up lists of characters. Every such list consists 

 of tw^o parts. The first half embodies the characters 

 which had been acquired up to the time when the sys- 

 tematic group, to which the plant belongs, originated, 

 and this part is therefore the same for every species 

 wnthin the group. The second half contains the later 

 characters, viz., those of the phylum and orders down to 

 the species and varieties. In drawing uj) such lists, it 

 is easy to reach the number of a few hundred characters: 

 but then the task becomes more arduous, and finally in- 

 superable difficulties are encountered. But it is evident 

 that even a complete list would scarcely embrace more 

 than a few^ thousand characters for any single plant. 



Our conclusions may therefore be summarized in the 

 follown'ng theses : 



^ ItifracelluJarc Pangcucsis (Gcr. c(\.) , p. 7: Englisli tratislntion 

 by Prof. C. Stuart Gager, 1910, p. 8. 



^ Loc. c'lf.. p. 24^. 



