ioo Chodcit. — On the Polymorphism of the Green 
To know some, or even all, of the constant characters only 
is in no way sufficient ; because if they are absolutely constant, 
the groups which are endowed with them become very sharply 
delimited, and their relation with other groups is very obscure, 
as for instance in the Characeae. It is only when we find 
representatives in which the important characters are altered 
or combined with peculiarities recalling other groups that we 
are able to put forward a theory as to the affinity of the 
family. The theory will be of no value until the induction 
drawn from comparative morphology leads us to find in the 
general life-history of the organism some gradual analogy 
showing a very definite tendency. 
Thus, for instance, in the Archegoniatae the archegonium 
and antheridium (putting aside the details of their organiza- 
tion) are very constant characters ; whereas we see in the 
reduction of the number of spores, or the progressive reduction 
of the prothallium, analogies tending to a very definite end. 
In natural groups there are sometimes concomitant characters 
which may not perhaps be mutually dependent but which 
generally vary at the same time. Every peculiarity is, as we 
know, susceptible of more or less change, sometimes so much 
so that it becomes not apparent, but only potential. Thus, 
for instance, a plant apparently destitute of leaves may bear 
them when circumstances are more favourable ; this is an indica- 
tion that the want of leaves is only an adaptive character. In 
some cases the leaves are only found in the younger stages, 
the plant being afterwards entirely destitute of them. In this 
case the evolution or life-history of the plant in its totality 
will be necessary in order to determine its affinities. 
For this reason I hoped to derive some fresh information 
from the variability, or, as it has been often called, the 
polymorphism, of the lower Chlorophyceae. 
The theory 1 put forward in this paper is the result of 
a great many observations extending over several years, on 
1 See also Chodat et Huber, Remarques sur le systeme des Algues vertes 
inferieures, Archives Sc. Phys. et Nat. Geneve, t. 31, p. 395. 
