430 



A TEXTBOOK OF BOTANY 



[Ch. X 



or on wet, shaded ground. They have all in common the 

 notable feature that the plant body, no matter how large 

 and elaborate, consists of a single tubular compartment 

 lined by protoplasm containing numerous nuclei and chloro- 

 plasts. Such a structure, morphologically equivalent to a mul- 

 ticellular individual in which the cross walls do not form, but 

 physiologically acting as a single multinucleate cell, is called a 

 ccenocyte. As in all such huge cells, protoplasmic streaming 



is active and evi- 



dent 

 Some 



(page 37). 

 300 species 



Fig. 298. — Vaucheria sessilis. 



Center, ccenocy tic filament, with cell forming a 

 zoospore ; and the zoospore, above. Below, an 

 oogonium and antheridium on a filament : all 

 X 150. 



are known, none, 

 however, having 

 economic utility. 



A common and 

 typical form is the 

 Green Felt or Vau- 

 cheria (Fig. 298), 

 of which the branch- 

 ing, green, tubular 

 filaments, some- 

 times attached by 

 colorless holdfasts, 

 interlace to a coarse 

 felt on the bottom of shallow waters, or on wet ground. 

 It occurs also on shaded, neglected soil or flower pots in green- 

 houses, whence is commonly drawn the material for labora- 

 tory studies. It reproduces asexually by zoospores, which 

 are multiciliate and multinucleate, and so large as to be 

 visible to the naked eye ; for each one is formed from the entire 

 contents of the end of a filament cut off by a cross wall. 

 After swimming about for a time, they come to rest and form 

 new filaments. The sexual reproduction presents features 

 not found in lower forms. A short branch grows out laterally, 

 a cross wall cuts off its contents, and the resultant cell de- 

 velops into a swollen oogonium containing a single egg cell, 



