THALLOPHYTES 



35 



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 



Figs. 95-97- — Vauchsria: showing forma- 

 tion (95), escape (96), and germination (97) of 

 zoospore. — After Coulter. 



Fig. 94. — Vanchcria : a small portion 

 of the filamentous, branching, coenocytic 

 body. 



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 Vau- 

 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 

 egg (oosphere) is formed. This 

 egg at first is multinucleate, but 



