250 



Heterokontce 



Family 1. CHLOROTHECIACE^. 



In this family the plants are very small, unicellular, gregarious, 

 or colonial. The solitary and gregarious cells are attached each by 

 a basal stalk, generally to some larger filamentous Alga, but in 

 the colonial forms the cells are united by mucilaginous bands or 

 stalks. Each cell contains a single nucleus and one or many 

 parietal chromatophores. Multiplication takes place in some 

 genera by vegetative division, but not in others. Reproduction 

 occurs by zoogonidia and isogamous gametes, with one long cilium 

 arid most probably a shorter one, the presence of which has not yet 

 been ascertained. 



The three following genera are known as British : 



A. Cells stalked ; no vegetative division. 



* Cells gregarious, living in the mucilaginous invest- 

 ments of other Algae and attached by a stalk of 

 extreme tenuity ; with one chromatophore Stipitococcus. 



** Cells ovoid, rounded, or ellipsoid, attached by a thick 



stalk ; chromatophores several or many Characiopsis. 



B. Cells united to form branched colonies by tubular 



stalks of mucilage; vegetative division abundant... Mischococcus. 



Genus Stipitococcus West & G. S. West, 1898 1 . The cells are 



very minute, gregarious, and 

 epiphytic on other filamentous 

 Alga3, being embedded in the 

 mucilage surrounding the fila- 

 ment, to which they are attached 

 by long stalks of extreme fine- 

 ness. In shape the cells are 

 ovoid and apiculate, or somewhat 

 campanulate, with a rounded 

 base and an attenuated or ir- 

 regularly expanded apex. There 

 is a single parietal chloroplast of 

 a pale green colour, somewhat 

 irregular in form and curled 

 round the inner surface of the 

 cell- wall. A single small nucleus 

 is present in the centre of the cell. Reproduction is by zoogonidia, 



1 West & G. S. West in Journ. Bot. Sept. 1898. 



Fig. 116. Stipitococcus urceolatus 

 W. & G. S. West ; A C, epiphytic on 

 a filament of Mougeotia, from Oughter- 

 shaw Tarn, W. Yorks. ; A, x500; B 

 and C, x 780 ; D, epiphytic on Sphtero- 

 zosma excavatwn, from Harris, Outer 

 Hebrides (x500). 



