420 



A TEXTBOOK OF BOTANY 



[On. X 



decay of the parent. Other cells enlarge and produce 

 egg cells or sperm cells, and fertilization occurs inside 



the cavity. Thus are 

 produced rough-walled 

 resting oospores, which 

 later germinate to new 

 plants. 



Ecologically the Pro- 

 tococcales are typical mi- 

 cro-hydrophytes, either 

 swimming, drifting, or 

 adherent ; and the latter 

 can also exist on the 

 land. Phylogenetically, 

 they are very closely and 

 obviously related to the 

 Flagellates, from which 

 they seem clearly de- 

 rived, the non-motile 

 forms being developed 

 from the motile by loss 

 of the cilia. 



ORDER 2. CONFERVA- 



LES.' THE CONFERVOID 



ALGM. These are the 

 largest and most familiar 

 of the Green Algae, in- 

 cluding the hair-like and 

 moss-like kinds of fresh 

 water, and filmy forms 

 of the sea coasts. Some 

 750 species are known, 



but none have economic importance. 



Typical of the simpler forms is the common Ulothrix 



(Fig. 289), which is one of the kinds forming dense, pilose, 



Right, 



FIG. 289. Ulothrix zonata. 



Left, young filament, X 300. 

 above, part of a filament showing escaping 

 zoospor'es, and below, another part showing 

 escaping gametes, with stages in conjuga- 

 tion, and zygospores ; lower, left, zygospore 

 in later stage, and right, after division into 

 zoospores; all x 482. (After Dodel-Port, 

 from Strasburger.) 



