2] 



THE VARIOUS GROUPS OF PLANTS 



31 





Fig. 5. — Some forms of Green Algae (Chlorophyceae). A, Pleurococcus — unicel- 

 lular, non-motile ( 2470); B, Chlamydomonas — unicellular, motile (x about 

 500); C, Pleodorina, colonial, motile ( ■ 250); D, cells from a filament of Ulothrix 

 (X 462); E, Enteromorpha intestinalis, a relative of Ulva {see G) ( X 5); F, Chara, 

 a highly organized Stonewort ( < i); G, Ulva lactuca, a Sea-lettuce (x about f); 

 H, various Desmids ( < 220). 



or grouped into colonies. Advanced types are commonly attached to 

 some object and consist of filaments or more substantial branched 

 structures, or have the form of a flattened thallus (simple vegetative 

 body lacking differentiation into true root, stem, and leaf) that may 

 be several inches in diameter. Fig. 5 shows a range of different 

 Chlorophyceae ; they are not merely extremely diverse but also 

 appear to have undergone evolution along a number of different lines, 

 most of which have proved to be ' dead ends ', Here are included 

 the Desmids, which are freshwater forms consisting usually of a 

 single cell that is sharply marked off into two symmetrical (and often 



