CONFERVOIDEJ;. 



57 



Fertilisation takes place in the following way. The oogonium 

 is a large ellipsoidal, swollen cell (og, in Fig. 54 A), whose contents 

 are rounded off into an oosphere with a colourless receptive-spot 

 (see B) ; an aperture is formed in the wall of the oogonium, through- 

 which the spermatozoids are enabled to enter (B). The sper- 

 matozoids are produced either directly, as in D (in pairs), in basal 

 cells of the filament, or indirectly. In the latter case a swarm- 

 spore (androspore) is formed which comes to rest, attaches itself 



FIG. 55 Coleochcete pulvinata. A A portion of a thallus with organs of reproduction; 

 a oogonium before, b after fertilisation; can antheriditim, closed; ci open, with emerg- 

 ing spermatozoid. B Ripe oogonium, with envelope. G Germination of the oospore. D 

 Zoospore. E Spermatozoid. 



to an oogonium, germinates, and gives rise to a filament of a very 

 fe\v cells dwarf-male (A, B, m). The spermatozoids are formed 

 in the upper cell of the dwarf-male (m), and are set free by the 

 summit of the antheridium lifting off like a lid. On the germina- 

 tion of the oospore ((7), which takes place in the following spring, 

 4 zoospores are produced (F) (i.e. the sexual generation) ; these 

 swarm about for a time, and ultimately grow into new filaments. 



Order 7. Coleochaetaceae. The thallus is always attached, 

 and of a disc- or cushion-shape, formed by the dichotomous 

 branching of filaments of cells united in a pseudo-parenchy- 

 matous manner. Each cell has only one nucleus. Asexual re- 

 production by zoospores with 2 cilia (Fig. 55 D), which may 

 arise in all the cells. Sexual reproduction by oogamous fertili- 

 sation. The spermatozoids resemble the swarmspores, but are 



