Characiese 



213 



the bristle (or seta) arises from the base of the cell and passes upwards along 

 a lateral groove, but in D. britannica G. S. West ('12) it is dorsal in its 

 attachment. Reproduction occurs only by biciliated zoogonidia (fig. 139 (7), 

 formed 4 to 32 in a mother-cell, and liberated in D. reniformis by the detach- 

 ment of a special lid. 



Fig. 139. Dicranochsete reniformis Hierouyrnus. x 1170 (after Hieronynms). A, cell showing 

 dichotomously branched bristle. B, cell showing the cushion of mucilage (m) in which it is 

 lodged and by which it is attached ; n, nucleus ; py, pyreuoids. C, zoogonidium. 



Sub-family CHARACIE^<:. The Alga? included in this small group are 

 unicellular and generally occur as epiphytes, either solitary or in clusters, on 

 other larger Alga?. The vegetative cells are rounded or angular in Sykidion 

 (fig. 141 F and G), but in the other genera they are distinctly stalked, in 

 which case there is a differentiation into base and apex. The largest cells 

 (up to 1 mm. in length when mature) are met with in Codiolum, in which the 

 cell-body is ovoid and the base drawn out into a solid stalk of some length. 

 In Characium (fig. 140) the cells are ovoid or fusiform, sometimes of consider- 

 able length, and in most cases asymmetrical. The basal stalk is in some 

 species so short that the cell appears to be sessile, whereas in others it is long 

 and slender. It is provided with a disc for attachment to the host, or more 

 rarely with minute rhizoidal outgrowths. The apex of the cell is often 

 acuminate and may be drawn out into a long apiculus. 



Each cell contains a single parietal chloroplast, except in Characiella, in 

 which the chloroplast is axile with short radiating processes and a central 

 pyrenoid. In Characium the chloroplast is very massive, filling most of the 

 cell, but in Sykidion it is more or less cup-shaped. A single pyrenoid is 



