ULOTHRIX ZONATA 43 



heat and provides for the future of its kind, in spite of 

 temporarily adverse conditions. When the zygotes 

 germinate, in late autumn or winter, they first produce 

 from two to fourteen cells, each of which may develop 

 into a separate filament, or thallus, or they may develop 

 zoospores that will ultimately settle down and grow into 

 filaments. 



We have outlined the general life-history of Ulothrix 

 zonata, and I do not propose to adduce some further 

 facts that, while interesting, are subsidiary, and would 

 probably confuse the theme. It should, however, be 

 mentioned that gametes which have been luckless in 

 securing partners may germinate like zoospores — a clear 

 case of parthenogenesis (Gr. parthenos, a virgin; genesis, 

 production). Further emphasis must be laid on the 

 fact that gametes from the same mother- cell do not 

 conjugate; marriage can take place only among gametes 

 from different cells. In this respect we have an instance 

 of that cross-fertilization which is so frequent in the 

 higher flowering plants. 



Ulothrix, then, displays sexual reproduction by means 

 of free-swimming gametes which are not sexually 

 differentiated; we cannot say which is male or which is 

 female. The sexual process is simple and primitive, 

 yet it is obviously different in some details from that 

 displayed in Sfirogyra and the Conjugatee in general. 

 Spirogyra gametes are not ciliated; they do not break 

 away and seek the freedom of the water, but they fuse 

 within the shelter of a cell- wall. 



Let us now examine our second example of the Con- 

 fervoideae, the genus (Edogonium. This genus includes 

 numerous species, some of which are among the com- 



