472 BOTANICAL GAZETTE [December 



The plastids in the zoospore mother cell seem always to be 

 multiplying in number during these nuclear divisions. When the 

 nucleus is in prophase of the first division, the surrounding cyto- 

 plasm contains a number of plastids in various stages (fig. 191) ; the 

 number is increased at the time of the 4-nucleate stage (fig. 192), 

 and at the 8-nucleate stage the cell is filled completely with the 

 plastids (fig. 193). It seems probable that this gradual multi- 

 plication of plastids may be one of the reasons why the zoospore 

 mother cell constantly increases in size up to the formation of the 

 zoospores, when the length of the mother cell becomes six times its 

 width. 



When the zoospore mother cell has reached the 8-nucleate 

 stage, cleavage furrows generally occur in the cytoplasm, and divide 

 the contents of the mother cell into 8 zoospore primordia (Anlagen). 

 Not infrequently, however, one or two more divisions occur after 

 the third, and as a consequence there are produced 16 or 32 nuclei, 



formed 



mother 



mechanism of the cleavag 



, zoospores is noteworthy. The 

 plastids at this time are arranged mostly near the cell membrane, 

 and the central part of the cell is occupied by the vacuolated cyto- 



asm(fig. 194). 



phery 



midst of the cytoplasm. There is first a movement of the nuclei, 

 and this is followed by a movement of the plastids; that is, the 

 8 nuclei are distributed to certain portions, not very close to the 

 periphery, and then a number of the plastids move toward one of 

 the nuclei as a center and surround it (fig. 195). Then there begins 



Hautschicht from 



asm 



formatio 



acuoles arranged 



in a cleavage line, which unite afterward and break up, leaving 

 the furrow in their places (fig. 196). As the result of the process 

 of the cleavage furrow, there are produced free independent zoospore 

 primordia packed close together within the mother cell (figs. i9 8 > 

 199). The relative position of the zoospores thus produced is 

 determined by the position the nuclei had occupied before the 

 cleavage began. Some of them are shown in fie. 1*. 



