ALGAE 49 
them respectively a more or less pronounced red or 
brown color. On this basis of color, the three classes 
are denominated the Green Algze (Chlorophycee), 
Brown Alge (Phzophycee), and Red Algze (Rhodo- 
phycee). While, at first sight, it would seem that 
such a classification is an artificial one, it is found, on 
more careful study, that these color differences are 
associated with constant and characteristic differences 
of structure, which really make the division a very 
natural one. Of these three classes, the two latter are 
mainly marine, and the peculiarities and color and 
structure are, with little question, largely the result of 
their peculiar environment. 
THE GREEN ALG (Chlorophycee) 
The Green Alge are for the most part fresh-water 
plants, and although most of them are more compli- 
cated in structure than the very simple Protococcacee 
and Volvocinee, still as a whole the members of the 
class are of simple structure, and, so far as the vege- 
tative parts are concerned, much inferior to their 
larger red and brown relatives. In spite of the low 
organization of the green alge, it is among these, 
rather than among the more complicated and larger 
marine red or brown ones, that we must look for the 
ancestors of the lowest green land plants, —the Mosses, 
—as there is strong evidence that these originated from 
aquatic plants allied to certain existing green alge. 
In spite of their simplicity, the latter show a consid- 
erable degree of variation among themselves, both as 
to their vegetative and reproductive parts, and upon 
E 
