312 



THALLOPHYTES 



duce a new plant directly but, as in Hydrodictyon, 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 ways 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 directly. 



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- 



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 Oedo- 

 gonium Huntii, 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. 



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 fertilize the eggs and 

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



