ULOTHRIX. 73 



and development of the zygospore, since it undergoes 

 a period of rest during the summer months, and 

 its progress is very slow during the succeeding 

 winter. 



Preparations showing active zoospores should be 

 treated with iodine solution, by which they will be 

 killed, and the observation of the cilia will be easy 

 by reason of the staining : note the four cilia in the 

 macro-zoospores, while there are only two in those 

 micro-zoospores which have not conjugated. 



Trace the processes of change in the cells of the filament pre- 

 ceding the escape of the zoospores : according to Dodel and others 

 their formation is by a process of cell-division : Strasburger, 

 however, states that the process is simultaneous ; being a case of 

 free cell-formation, preceded, however, by a process of nuclear 

 division (see Zellbildung, 1880, page 75). 



