THALLOPHYTES 



35 



FIG. 94. Vaucheria: a small portion 



* e filamentous branching, coenocytic 



Zoospore. The asexual reproduc- 

 tion is modified in an interesting way 



by the coenocytic habit. At the tip 



of a branch a very large zoospore is 



formed by the protoplast, and is cut 



off from the general body by a wall 



(fig. 95). It is discharged through 



an opening at the end of the branch 



and moves actively by means of cilia 



that are distributed over its whole 



surface (fig. 96). The zoospore is 



multinucleate, containing the nuclei 



that were in the end of the branch at 



the time of its formation, and in con- 

 nection with each nucleus a pair of 



cilia is formed. This large zoospore, 



therefore, may be regarded as a com- 

 pound zoospore, corresponding to a 



number of biciliate zoospores. It germinates directly, producing a 



new filament (fig. 97). 



Sexual reproduction. The 

 structures connected with sexual 

 reproduction are more highly 

 developed than any previously 

 mentioned, for not only is Van- 

 cheria heterogamous, but it pro- 

 duces special sex organs which 

 are not transformed vegetative 

 cells, but are specifically for 

 gamete-production from the be- 

 ginning. In one of the species, 

 for example (fig. 99), a special 

 branch is put out from the side 

 of the filament, and a terminal 

 cell is cut off by a wall and en- 

 larges into a more or less globular 

 oogonium, in which a single large 

 FIGS. 95-97- - Fa^rx: showing forma- ( oosph ere) is formed. This 



tion (95), escape (96), and germination (97) of c && V 



zoospore. -After CJULTE*. egg at first is multmucleate . but 



