68 



Chlorophycece 



Some of the cells are furnished with a colourless bristle which is 

 fixed at its base into a narrow sheath of considerable length. 

 / Asexual reproduction takes place by means of large ovoidal 

 zoogonidia (fig. 17 D), furnished with two long cilia and produced 

 singly from the cells of the thallus, more particularly from the 

 terminal cells of the branches. The zoogonidium escapes from 

 the zoogonidangium either by a round orifice on the upper surface 

 or by the dissolution of the extremity of the terminal cell. 



Sexual reproduction is brought about by the fertilization of an 

 oosphere by an antherozoid. The sexual organs are oogonia and 



Fig. 17. Coleochcete pulvinata A. Br. A and B, from near Glenties, Donegal, Ireland ; 

 A, portion of thallus with sexual organs ( x 460) ; o, oogonium ; t, trichogyne ; 

 a, antheridia. B, ripe ' spermocarp ' emitting the cells formed by the division 

 of the oospore ; each of these becomes a zoospore ( x 460). C, zoospore (after 

 Chodat). D, zoogonidium (after Pringsheim). 



antheridia. The oogonium is developed by a swelling of the 

 terminal cell of a branch and it possesses on its upper surface a 

 narrow trichogyne. An oosphere containing chlorophyll is pro- 

 duced within the oogonium, and just previous to fertilization the 

 trichogyne opens at the apex and exudes a colourless drop of 

 mucilage. The antheridia are flask-shaped cells which are developed 

 from cells in the neighbourhood of the oogonium, or in direcious 

 species from cells of another thallus. Only one antherozoid is 



