172 PHYLUM II. CIILOROPHYCEAE 



sites (Family Synchytriaccae) in the tissues of other algae, 

 or even land plants, and are known as Gall-fungi. 



ORDER COENOBIALES 



238. The cells or coenocytes in these plants are aggre- 

 gated into colonies, the most common of which are the 



pretty species of Scenedesmus, in 

 which four spindle-shaped cells lie 

 side by side. Less common is the 

 very regular plate-colony of Pedias- 

 trum with usually a dozen or more 

 regularly arranged coenocytes. Re- 

 T, ^^ o , lated to these is the Water Net 



riG. GG. — Scenedosmus, 



dfcf'oi'"™ ''"'^ Hydro- (Hydrodictyon) with its many long 

 coenocytes arranged in a hollow, 

 reticulated colony 20 to 30 centimeters long. Ciliated 

 zoospores and isogametes occur in Pediastrum and 

 H3xlrodictyon. 



239. Here are commonly placed certain doubtful 

 organisms, the Volvoces (Volvox, Pandorina, and related 

 genera), with the color of plants but the structure of 

 animals. Most botanists still claim them on account of 

 their color, but many zoologists emphasizing the impor- 

 tance of their structure regard them as animals (Flag- 

 ellata). The explanation here given is that at about 

 this point in the Vegetable Kingdom the animal type be- 

 came differentiated from the plant type by an increase 

 in the motility of the cells, and in the Volvoces we have 

 the organisms on the pathway leading from plants to 

 animals. In the opinion of the authors they have already 

 passed the frontier of the Plant Kingdom, and entered 

 that of Animals, although they have not yet abandoned 

 their use of chlorophyll. 



240. On the same ground should be excluded the ''red 



