270 



PLANT LIFE. 



plants, though the small ones produce very slender, weak fila- 

 ments (fig. 302). Beside the zoospores, Ulothrix produces, 

 under certain conditions, gametes, which are precisely like 



FIG. 301. Ulothrix zonata. A, a young filament with rhizoid cell, r, at base. B, bit 

 of a filament from whose cells large zoospores are escaping through a pore in the side- 

 wall. C, a single large zoospore. D, bit of a filament from whose cells small zoo- 

 spores lor gametes) are escaping. , small zoospores (or gametes . F, gametes con- 

 jugating. G, same, conjugation complete. //, zygote, before formation of wall to 

 become a resting spore. Magnified 482 diam. After Dodel-Port. 



the small zoospores in appearance. But their behavior is 

 different. They usually conjugate freely in pairs and produce 

 resting spores. If, however, they do not conjugate, each 



