Protococcacece 215 



Genus Sorastrum Kiitz., 1845. [Selenosphcerium Cohn, 1879.] 

 The ccenobium is globose, consisting commonly of 16 to 64 (rarely 

 4 or 8) stalked cells, the 

 stalks uniting in the 

 centre of the coenobium 

 to form a small faceted 

 sphere. In small colonies 

 the stalks of the cells are 

 very short and the central 

 sphere is not always ap- 

 parent. The cells are 



Fig. 89. Sorastrum spinulosum Nag., A, 



broadly sublunate, reni- 8ma ll ccenobium from Pilmoor, N. Yorks. ( x 475); 

 form or subtrianerdar in B, large ccenobium from Clifden, Galway, Ireland 



( x 450). 

 shape, and each extremity 



is furnished with two spines (rarely one) of moderate length. 

 There is one chloroplast, containing a pyrenoid, in each cell. 

 The multiplication is by the formation of autocolonies, but the 

 details have not been worked out. 



The British species usually met with is S. spinulosum Nag. ; diam. of 

 ccenobia 31 90 /*; length of cells without spines 11 26 /i; fig. 89. It is a 

 scarce plant occurring in bog-pools or amongst aquatic Phanerogams in the 

 quiet margins of lakes. S. Americanum (Bohlin) Schmidle occurs in the 

 freshwater plankton of the Outer Hebrides. 



Sub-family II. CRUCIGENIE.E. 



The ccenobia consist of few or many cells regularly arranged in 

 the form of a flat plate. The cells are very variable in form, 

 generally somewhat rounded, and occasionally furnished with spines. 

 They are disposed in groups of four, the latter being held in 

 position by a tough mucilage. In some the chloroplasts possess a 

 single pyrenoid, but in others pyrenoids are absent. 



The multiplication is by autocolonies, which in some cases are 

 set free almost immediately, but in others remain for some time as 

 part of the mother-colony. 



Genus Crucigenia Morren, 1830. [Staurogenia Klitz., 1849 ; 

 Lemmermannia Chodat, 1899 ; Willed Schmidle, 1900.] The 

 coenobium consists of 4, 8, 16, or 32 cells arranged as a flat plate 

 and held in position by a mucilaginous envelope, but under 

 favourable conditions of environment as many as 128 cells have 



