350 Myxophycece 



and are densely aggregated to form solid colonies of variable 

 shape. In some species the colonies are globose, ellipsoidal, or 



oblong ; in others they are 

 much elongated ; and in 

 others they become ela- 

 thrate and almost anasto- 

 mosing. The cell-contents 

 are blue-green, olive-green, 

 or rose-purple in colour, 

 and often contain gas- 

 B vacuoles. 



Fig. 164. A, Microcystis stagnalis Lemm., M. marginata Menegh. 



from the plankton of Lough Neagh Ireland. (diftm< of cells 2 -6 2'8/i; fig. 

 B, M. marginata Menegh., from Old Cote 



Moor, W. Yorks. ( x 450). 164 B )> M - flos-aquce (Wittr.) 



Kirchn., N. elabens (Breb.) 



Kiitz., and M. stagnalis Lemm. (diam. of cells 1 1'5 p. ; fig. 164 A) are all more 

 or less common in bogs and lakes. M. roseo-persicinus (Kiitz.) often occurs 

 in quantity in ponds and ditches which contain much decaying vegetation. 

 M. ceruginosa (Kiitz.) [ = Clathrocystis ceruginosa (Kiitz.) Henfrey] often occurs 

 in prodigious quantity in ponds and in the plankton of lakes. 



The three genera Microcystis, Polycystis and Clathrocystis are not suffi- 

 ciently distinct to warrant their separation. The differences between them 

 are only differences of degree. 



Genus Gloeocapsa Ktitz., 1843 ; em. Nag. 1849. The cells are 

 globose and furnished with a thick integument, which is frequently 

 lamellose. The daughter-cells which arise by the division of the 

 mother-cells are generally retained as part of the colony, a larger 

 integument surrounding the individual envelopes of the cells. In 

 this manner the colonies become of large size and frequently form 

 a gelatinous stratum. The integuments of the cells are sometimes 

 colourless, but they may be yellow, brown, blue, violet, or red. 

 Cell-division takes place in all directions and the colonies are 

 most irregular. Thick-walled resting-spores have been observed 

 in some species. 



Kuntze and, following him, certain other authors, have identi- 

 fied Gloeocapsa Kiitz. with Bichatia Turp. (1827), but to my mind 

 this identification is uncertain. 



There are about 20 British species, some of which are of doubtful specific 

 distinctness. Gl. punctata Nag. (diam. of cells 1'5 2/x) is the smallest 

 species. Gl. polydermatica Kiitz. is remarkable for the larnellatiou of the 

 integuments (fig. 165 C E). Gl. Magma (Breb.) Kiitz. with golden-yellow or 



