200 



Chlorophycece 



single parietal chloroplast in each cell, generally of considerable 

 extent and containing one pyrenoid. 



There is no vegetative division. 



Reproduction takes place by the formation of numerous 

 zoogonidia in each cell. There is a repeated division of the cell- 

 contents, several transverse divisions occurring before the first 

 longitudinal division, and in a short time each portion loses its 

 angular character, becomes rounded off, and forms a biciliated 

 zoogonidium. The escape of the zoogonidia takes place either by 

 a lateral or a terminal aperture. The pyrenoid disappears (in 

 some species) during the formation of the zoogonidia, and reappears 

 on their germination. Each zoogonidium on coming to rest 

 develops into a new plant. 



Genus Characium A. Br., 1849. [Hydrocytium A. Br., 1855 ; 

 Hydrianum Rabenh., 1868.] The cells are fixed by a basal stalk, 



Fig. 80. A and B, Characium Pringsheimii A. Br. ; A, from Mitcham Common, 

 Surrey; B, attached to a frustule of Tabellaria Jiocculosa, from Gunwen Moor, 

 Cornwall. C, Ch. subulatum A. Br., from Wimpole Park, Cambridgeshire. 

 D, Ch. ensiforme Herm., from Pilmoor, N. Yorks. (All x 520.) 



usually rather short, but sometimes much elongated ; in form they 

 are spherical, ellipsoid, oblong, or fusiform, and they are generally 

 asymmetrical. The cells as a rule give rise to 16 or 32 

 zoogonidia. 



Some eight or ten species of the genus are known to occur in Britain, of 

 which Ch. Sieboldii A. Br. (length 40 70 p. ; diam. 20 33 /*), Ch. ambiguum 

 A. Br. (length 1530^; diam. 2'5 4 /x), Ch. Pringsheimii A. Br. (length 

 18 35 p.; diam. 5 ITS p; fig. 80 A and B) and Ch. ornithocephalum A. Br. 

 (length 19 33 p.; diam. 8 12*5 /*) are the most general. Ch. ensiforme Herm. 

 (length 65 86 /* ; diam. 2'5 3'8 p ; fig. 80 D) is the most elongate species of 

 the genus. 



