ALG^ 49 



them respectively a more or less pronounced red or 

 brown color. On this basis of color, the three classes 

 are denominated the Green Algee (Chlorophycese), 

 Brown Algae (Phseophyceee), and Red Algae (Rhodo- 

 phyceae). 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^ (^Ohlorophyeece) 



The Green Algae are for the most part fresh-water 

 plants, and although most of them are more compli- 

 cated in structure than the very simple Protococcaceae 

 and Volvocineae, 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 algae, 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 algae. 



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 



