THE GEEAT GROUPS OE ALG^E 



243 



plasm organized about it is a cell, whether it has a wall or 

 not. Therefore the body of Vaucheria is made up of as 

 many cells as there are nuclei, cells whose protoplasmic 

 structures have not been kept separate by cell walls. Such 

 a body, made up of numerous cells, but with no partitions, 

 is called a cmnocyte, or it is said to be ccenocytic. Vaucheria 

 represents a great group of Chlorophyceas whose members 

 have ccenocytic bodies, and on this account they are called 

 the Siphon forms. 



Vaucheria produces very large zoospores. The tip of a 

 branch becomes separated from the rest of the body by a 

 partition and thus acts as a sporangium (Fig. 208, B). In 

 this improvised sporangium the whole of the contents or- 

 ganize a single large zoospore, which is ciliated all over, 

 escapes by squeezing through a perforation in the wall 

 (Fig. 208, C), swims about for a time, and finally 

 develops another Vaucheria body (Figs. 208, E, 

 209). It should be said that this large body, 

 called a zoospore and acting like one, is really 

 a mass of small biciliate zoospores, just as the 



Fig. 209. A young Vaucheiia germinating from a 

 spore (sp), and showing the holdfast (w). — 

 After Sachs. 



apparently one-celled vegetative body is really composed of 

 many cells. In this large compound zoospore there are 

 many nuclei, and in connection with each nucleus two cilia 

 are developed. Each nucleus with its cytojilasm and two 

 cilia represents a small biciliate zoospore, such as those of 

 Cladophora, §165. 



Antheridia and oogonia are also developed. In a com- 

 mon form these two sex organs appear as short special 

 branches developed on the side of the large ccenocytic body, 



