The Biochronlc Equation. 673 
extraordinary richness of its forms, from a relatively 
small number of elementary units, for almost every indi- 
vidual character is found in numerous species, and it is 
to their different grouping and their combination with 
the rarer factors that the extraordinary diversity of liv- 
ing forms is due. 1 
As we can easily see, this view effects a considerable 
simplification of the problem. Many 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. 2 
The question is, however, how many elementary char- 
acters an angiosperm or a higher animal possesses, on 
the average. In the former case I have attempted to 
draw up lists of characters. Every such list consists 
of two 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 
within the group. The second half contains the later 
characters, viz., those of the phylum and orders down to 
the species and varieties. In drawing up 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 
following theses : 
1 Intracellularc Pangenesis (Ger. ed.), p. 7; English translation 
by Prof. C. STUART GAGER, 1910, p. 8. 
2 Loc. cit., p. 24%. 
