214 



Chlorococtineae 



present in each of these genera. In Codiolum the chloroplast is reticulate 

 with radial ingrowths, and contains several pyrenoids. In none of the genera 

 is there more than one nucleus. 



Vegetative cell-division is unknown. Reproduction occurs by the forma- 

 tion of zoogonidia through the division of the contents of the mother-cell, 

 by either successive or simultaneous division-planes. As a rule several 

 transverse divisions occur before the first longitudinal division, and in a short 

 time each portion loses its angularity, becomes rounded off and forms an ovoid 

 zoogonidium. In tii/kidion there are 2 or 4 zoogonidia formed in each mother- 

 cell (fig. 141 F), but in CJiaracium and Codiolum there are 16 or 32. The 

 zoogonidia are biciliated in all except Codiolum in which they are furnished 



Fig. 140. A aud B, Chamcium Prlnf^lieimn A. Br. B is attached to a cell of Tabellaria 

 focculosa. C, Ch. xtibulntum A. Br. D, Ch. ensiforme Herm. All x 520. 



with 4 cilia. The zoogonidia escape by either a terminal or a lateral 

 (fig. 141 D) aperture, and on coming to rest at once germinate to form new 

 plants. In some species the pyrenoid disappears during the formation of 

 zoogonidia, pyrenoids being developed de novo in the young plants. In 

 Codiolum biciliated gametes have been recorded, but they have not been 

 observed to conjugate and must be regarded as doubtful. Aplanospores are 

 known in Sykidion (fig. 141 G) and in Codiolum. 



Characium is a common genus of freshwater Algse, occurring as an epiphyte on various 

 species of (Edogonium, Vaucheria, Cladophora, and other filamentous Algae, often so 

 thickly as completely to hide the host-plant. The gregarious habit is, of course, associated 

 with the method of reproduction, large numbers of zoogonidia coming to rest in one place 

 and germinating simultaneously. Much the largest species of the genus seems to be Ch. 

 graciliceps Lambert ('10 A), which is epizootic on the Phyllopod Branchipus vernalis, the 

 cells attaining a length of 480 /x (fig. 141 A and B}. 



Codiolum is marine or inhabits brackish water, occurring as a thin stratum on rocks, 

 stones, the piles of harbours, and as a gregarious epiphyte on larger marine Algte. 

 Sykidion (with the possible exception of one species) is also a marine epiphyte. 



The genera are : Characium A. Brann, 1849 ; Codiolum A. Broun, 1849 ; St/kidion 

 Wright, 1879; ChftrnrMfa Schmidle, 1903. 



