Ch. X] 



THE GREEN ALG^J 



417 



described by arctic and alpine travelers/ Other kinds some- 

 times reproduce in such numbers as to form greenish clouds 

 in clear fresh water. Here also belongs Protosiphon (page 303) . 



Fig. 284. — Chlamydomonas Reinhardi ; showing sexual reproduction; 

 X 750. 



Above, left, adult individual ; next, one of the isogametas ; right, two 

 gametes in conjugation. The black spot is the red eye spot. Below, young 

 zygospore, the gametes not fully fused ; next, ripe zygospore ; right, germi- 

 nation of the zygospore into four new individuals. (After Goroschankin.) 



The most prominent and familiar of the non-motile kinds 

 is Pleurococcus, which forms the bright green coating, often 

 resembling remnants of green paint, on old shaded tree trunks, 

 stones, flowerpots, and 

 earth. The plant 

 body is a single spheri- 

 cal cell (Fig. 285) with 

 a large chromato- 

 phore. It reproduces, 

 so far as known, only 

 by fission, the new cells 

 remaining for a time irregularly in contact with the older, 

 to which, as to the substratum, they are bound by the 

 2b 



Fig. 285. — Pleurococcus vulgaris, from a 

 tnc trunk, showing division; X 1000. 



