312 



THALLOPHYTES 



duce ji new plant directly but, as in H^^drodictyon, produces 

 a number of zoospores each of which produces a new plant. 

 Thus, instead of one, a number of new plants arise from the 

 zygospore, a feature of advantage in the multiplication of new 

 plants. 



Another form, similar in a number of waj^s to Ulothrix, is 



Cladophora which has long 

 branched filaments that 

 form long, green, hair-like 

 tufts, which, with one end 

 anchored to a stone or some 

 other object, wave back and 

 forth in moving streams. 

 The cells are multinucleate 

 and contain many chloro- 

 plasts. Reproduction is by 

 zoospores and isogametes, 

 but .the zygospore develops 

 a new plant directlj^ 



Oedogonium. — This form 

 (Fig. 268), common in lakes 

 and ponds, is similar to Ulo- 

 thrix in the character of the 

 filament, but shows marked 

 advancement in methods of 

 reproduction. The z o - 

 ospores, formed only one in 

 a cell and consequently very 

 large, have numerous cilia 

 forming a crown at the for- 

 ward end. Sexual reproduc- 

 tion is distinctly heteroga- 

 mous. The eggs, which are 

 large and packed with food, 

 are borne in much enlarged 

 cells called oogonia. Each oogonium bears one egg and is simply 

 a transformed vegetative cell of the filament. Other small cells 

 produce the sperms which resemble the zoospores except in size. 

 The sperms swim to the oogonia, enter, and ff^rtilize the eggs and 

 thick-walled resting oospores are then formed. Upon germina- 



FiG. 268. — Oedogonium. A , a portion 

 of a filament of Oedogonium echinosper- 

 mum, showing some vegetative cells and 

 oogonium above and some antheridia be- 

 low from which sperms are escaping; B, a 

 portion of a female filament of OEDOGO- 

 NIUM HUNTIT, showing oogonia and 

 two dwarf male plants attached near the 

 oogonia; C, zoospores of an Oedogonium 

 escaping from the cells of the filament. 

 X about 300. Drawn from Wolle. 



