GREEN SLIMES 171 



236. This phylum has been unusually productive of 

 other phyla of primary and secondary rank, and the 

 suggestion is hazarded that also from it (near Proto- 

 coccoideae) a phyletic line gave rise to the Animal King- 

 dom. There are two classes: 



I. Plants unicellular, or in colonies. 



Class 3. PROTOCOCCOIDEAE 



II. Plants pluricellular, in filaments (or plates). 



ClaSS 4. CONFERVOIDEAE 



CLASS 3. PROTOCOCCOIDEAE. GREEN SLIMES 



236. These plants (of about 450 species) are nearly all 

 microscopic, and are unicellular, or in a few cases aggre- 

 gated into definite colonies. They propagate (reproduce 

 by asexual reproduction) by (1) cell division, (2) ciliated 

 zoospores, (3) and thick- walled spores (chlamydospores), 

 and generate (reproduce by sexual reproduction) by the 

 union of equal, motile gametes (isogametes) to form a 

 single cell (zygote) which often becomes a thick-walled 

 spore. Generation is not known for all of the species. 



ORDER PALMELLALES 



237. These unicellular plants are not aggregated into 

 colonies, although they may remain attached together 

 in irregular masses for some time after cell 



division. They are common in water, and 



in moist or wet places, as the sides of walls, 



trees, posts, etc., where they often form 



dense, green layers. The spherical forms 



growing on trees, walls, etc., which produce 



no zoospores are species of Protococcus, 



while those with zoospores may be Chlorococcum. 



Near relatives of these have become unicellular para- 



