CHAPTER V. THE THALLOPHYTA. 



293 



After fertilization, the oospore acquires a thick cell-wall, and 

 in ripening changes to a brown color. The oogonium, with the 

 ripened oospore still enclosed within its walls, now separates from 

 the filament which bore it, and the spore, after a period of rest, 

 germinates. It does not, however, immediately develop into a 

 filament, but the protoplasm of the spore first escapes into the 

 water enclosed within a mucilage, then the protoplasm divides 

 and forms four ciliated cells. These escape from the mucilag- 

 inous envelope, and, after moving about for a while, come to rest, 

 and each develops into a filament. 



og 



B an s 



Fig. 490. — A, part of fertile thallus ot Coleochaete puivinata (magnified 350 diameters). 

 og> og, og, oogonia in various stages of development ; an, an, antheridia ; z, s. anthero- 

 zoids : J, s, swarm-spores ; B, ripe oogonium in its cellular rind, r. After Pringsheim, 

 from Sachs' Botany. 



The Coleochaete. We may take Coleochaete pulvinata to 

 illustrate this group. It occurs as small rounded, dark-green 

 or olive-green masses, from T \ to \ an inch in diameter, attached 

 to stones, sticks or water-weeds in calcareous spring-waters. Each 

 mass consists of a number of articulated, branching filaments, 

 the cells composing which are oblong, narrower at the basal end, 

 more or less dilated anteriorly, and often provided with a trans- 

 parent hair or bristle, which has at its base a kind of sheath. 



The plants propagate themselves asexuafly by means of zoo- 

 spores, which may arise from any of the vegetative cells, and 



