228 



THE ALGAE 



tion. The last-named family differs from the other two in that some 

 members at least possess a regular alternation of generations and 

 there are differences in respect of the gonimoblasts and cystocarps. 

 In the uncorticated uniaxial Chantransiaceae the genus Acro- 

 chaetium is extremely widespread. Many of the species of Chan- 

 transia are now known to be phases in the life cycle of Batracho- 

 spermum species (see below). The marine Chantransia violacea and 

 C. effiorescens are said to have alternation of haploid and diploid 

 generations. In the genus Rhodochorton only the tetrasporic genera- 

 tion is known. Study of Ufe cycles may assist in solving some 

 problems and it is not urdikely that there are also problems of 

 synonymy. 



* Batrachospermaceae : Batrachospermum (batracho, frog; sper- 

 mum, seed). Fig. 125 

 Two genera commonly found in fresh waters, Batrachospermum 

 and Lemanea, belong to the Nemalionales. B. moniliforme, which is 

 a very variable species, is found attached to stones in swift-flowing 

 waters of the tropics and temperate regions. The thallus, which is 

 violet or blue-green in colour, is soft, thick and gelatinous, the 

 primary axis, which grows from an apical cell, being formed of a 



/ 



i 





W 



Fig. 125 Batrachospermum moniliforme. A, plant. B, portion of 



plant. C, carpogonial branch ( x 480). D, fertilized carpogonium 



( X 360). E, mature cystocarp ( x 240). F, antheridia ( x 640). (A, B, 



after Oltmannsi C-F, after Kylin.) 



