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 



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

 of a filament from whose cells large zoospore^ 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 (or gametes* are escaping. E, small zoospores (or gametes . F, gametes con- 

 t'ugatmg. G, same, conjugation complete. //, zygote, before formation of wall to 

 >ecome 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 



