Volvocacece 



189 



zoogonidia, four of which arise in a mother-cell by the double 

 transverse division of the contents. Sexual reproduction also 

 occurs by the fusion of isogamous or heterogamous gametes. 



Chi. euchlorum Ehrenb. (length up to 50 p breadth 8 12 /x) is apparently 

 a very scarce British Alga of which I have examined a few specimens from 

 stagnant ditches near the Lizard, Cornwall. 



Certidium elongatum Dang. (1888) would be more correctly placed as 

 another species of this genus. 



[Hcematococcus Ag., 



Fig. 74. A H. Sphce- 

 rella lacustris (Girod.) 

 Wittr., from Bradford, 

 W. Yorks. (x475). 



Genus Sphserella Sommerfeldt, 1824. 

 1828; Chlamydococcus A. Br., 1849.] The 

 cells are ovoid and very similar to those of 

 Chlamydomonas, but the cell-wall stands out 

 away from the cell-body, being connected to 

 it by delicate strands of protoplasm. The 

 chloroplast is bell-shaped and contains one 

 or several pyrenoids. The genus is scarcely 

 separable from Chlamydomonas, only differing 

 in the outstanding cell-wall and the absence 

 of contractile vacuoles, the zoogonidia being 

 exactly of the Chlamydomonadine type. 



Sph. lacustris (Girod.) Wittr. [Chlamydococcus 

 pluvialis (Flot.) A. Br.] is abundant all over the 

 country in ditches, rain-pools and bog-pools. The 

 cells, which frequently become brick-red in colour 

 owing to the presence of haematochromin, vary from 



8 to 30 p. in diameter ; they often become encysted, and the reproduction is 

 by zoogonidia and isogamous gametes (fig. 74). The curious phenomenon 

 known as "Red Rain" owes its colour in a few instances to the presence of 

 this Alga. Sph. nivalis Sommerf., which can scarcely be specifically distin- 

 guished from Sph. lacustris, is the " Red Snow " plant. 



Wille 1 has recently attempted to show that Hcematococcus is the correct 

 name of this genus, but I fail to see the reason for such a change. The remarks 

 made by Hazen 2 on the nomenclature of this genus should also be consulted. 



Sub-family II. PHACOTE^E. 



This sub-family is only distinguished from the Chlamydomo- 

 nadeae by the thick, solid cell-wall, which on the escape of the 

 daughter-cells during reproduction separates into two portions. 



1 Wille, 'Algologische Notizen X,' Nyt Magazin f. Naturvidenskab, Bd 41, 

 H. 1, Kristiania, 1903. 



2 Hazen, 'The Life-History of Sphcerella lacustris, 1 Mem. Torr. Bot. Club, vi, 

 1899, p. 236. 





