248 
PLANT STUDIES 
by walls, or they are coenocytic, as in the Siphon forms. 
The characteristic asexual spores are zoospores, but these 
may be wanting, as in the Conjugate forms. In addition 
to asexual reproduction, both isogamy and heterogamy are 
developed, and both zygotes and oospores are resting spores. 
FIG. 216. A group of Desmids, one-celled Conjugate forms, showing various pat- 
terns, and the cells organized into distinct halves. After KERNEB. 
The Green Algae are of special interest in connection 
with the evolution of higher plants, which are supposed to 
have been derived from them. 
3. PH^OPHYCE^; (Brown Algce) 
169. General characters. The Blue-green Algae and the 
Green Algae are characteristic of fresh water, but the Brown 
Algas, or " kelps," are almost all marine, being very charac- 
