100 FRESH-WATER ALG^. 



dance at the bottom of ponds or lakes, occasionally rising and 

 floating on the surface. 



Draparnaldia is recognised by its filaments being furnished 

 more or less densely with penicellate, fasciculate branchlets, alter- 

 nate or opposite, composed of smaller fertile cells. The terminal 

 cells of all the branches are empty, hyaline, and sterile, and more 

 or less elongated into a bristle. 



Class IV. — CARPospoREiE. 



This class, while possessing many points in common with the 

 class OosPOREiE, is nevertheless characterised by the formation of 

 the spore fruit, or sporocarp, which consists of two distinct parts, 

 viz., a fertile part, derived directly from the female organ, and 

 ultimately producing spores, and an investing part, which encloses 

 the spores until ripe, but which is relatively small and merely 

 appendicular in the fresh-water Algae, although attaining great 

 prominence in the Fungi. 



The ColeochcetecB are small discoid algce of a bright green 

 colour constructed of branched rows of cells, attached to the sub- 

 merged parts of other plants in the form of little circular masses. 

 The name of the genus is due to the fact of certain cells of the 

 thallus bearing colourless erect bristles. 



The reproduction is by a sexual zoogonidia and by resting 

 spores. The resting spores do not at once produce new plants, 

 but zoospores. The zoospores produced early in the year from a 

 sporocarp of the previous year, produce only asexual plants for 

 several generations. At length a sexual generation arises which 

 may be monoecious or dioecious, and fertilisation produces one 

 oospore in the carpogonia, which clothe themselves with a peculiar 

 layer of cortical cells, and the oospore itself developes into a 

 parenchymatous reproductive body, from the cells of which 

 zoospores proceed in the next period of vegetation. 



Batjachospert7iecR contains the two genera, Batrachospenmim and 

 Thorea. In Batrachospermum the thallus is moniliform, com- 

 posed of a simple series of medullary cells and a cortical accessory 

 parallel series, clothed with sub-globose clustered fascicles of 

 branches. 



In Thorea the thallus is filamentose, attenuated at the apex 



