CHAPTER VIII 

 PHYLUM II. CHLOROPHYCEAE* 



THE SIMPLE ALGAE 



232. The plants of this phylum while still small, and 

 mostly microscopic and consisting of single cells, fila- 

 ments or rarely plates of cells, show a considerable ad- 

 vance over the Slime Algae in having well-defined nuclei, 

 definite plastids, a dominant yellow-green color (chlor- 

 ophyll and carotin), and in many genera 

 sexual reproduction. The cells are much 

 better developed, the walls are composed of 

 cellulose, and are usually firmer. The nu- 



FiG. 64.— A clear matter of the cell is collected into a 



ropbyoeae!^'^'"' definite nucleus which is surrounded by a 



membrane. A portion of the protoplasm is 



set off as one or more distinct plastids (chloroplasts) 



which are stained green by chlorophyll. 



233. Here the dominant idea is the definite nucleus 

 limited by a nuclear membrane. With this are associated 

 the definite plastids, true chlorophyll, firm cell wall, 

 motile reproductive structures (zoospores and gametes), 

 and the still simple plant body. 



234. The Simple Algae, of which there are about 1100 

 species, are mainly fresh-water . plants, living on wet 

 rocks, moist walls or tree-trunks, etc., or floating or 

 attached in the deeper waters. A few have become 

 degenerated through parasitism. 



* This name is here used in the narrower sense, excluding the 

 plants of the phyla Zyqophyceae and Siphonophycbae. 



170 



