THE THALLOPHYTA 



271 



produces it (like all egg-producing structures in these lower 

 plants) is termed an odgonium. In other cells the contents divide 

 into two small, motile male gametes or sperms, and each of these 

 mother-cells (like all structures which produce male gametes) 

 is known as an antheridium. One of the sperms enters an egg 



Fig. 148. Fig. 149. 



Fig. 148 — Ulothrix. A, young filament with rhizoid cell (r) by which it is 

 attached. B, portion of filament with escaping zoospores. C, single zoospore. 

 D, formation and escape of gametes. E, gametes. F and G, stage in the 

 conjugation of two gametes. //, zygote or zygospore. I, zygote beginning to 

 germinate. J, group of zoospores produced by a zygote. (From Strasburger, 

 after Dodel-Port). 



Fig. 149. — Oedogonium nodulosum. A, filament with antheridium (a), each 

 cell of which produces two sperms; and oogonium (o), containing one large egg. 

 B, filament with a thick-walledo ospore {os) which has developed from a fertilized 

 egg. C, basal cell of a filament, showing holdfast. All X 300. 



and fertilizes it, and the oospore thus formed germinates into a 

 group of zoospores. 



Coleochaete (Fig. 150) is a fresh-water alga the vegetative body 

 of which consists of a flat plate or cushion of radiating filaments. 

 Its cells may produce single, large, biciliate zoospores. Antheri- 



