40 



Myxophycex 



something of a puzzle. The form of its cells, with strong cell-walls, and 

 the method of formation of the daughter-cells are exactly as in the Chloro- 

 phyceous genus Oocystis. It has a definite nucleus with a nuclear membrane, 

 and fully differentiated chromatophores of a rich blue-green colour (consult 

 fig. 24). In the young cells the chromatophores are numerous and short, 

 but in older cells there are from 10 to 20 of them, mostly curved, and 

 more or less radiating from the central part of the cell. 



(Jlaucocystis Nosiochinearum is not uncommon in bogs in Western Europe, and a large 



form of it has been found in E. Africa. There 

 is no doubt that the Alga differs from all the 

 other Blue-green Algse in the possession of a 

 higher type of protoplast and true chromato- 

 phores, and it was this fact which led to the 

 suggestion that the Myxophyceae should be 

 primarily divided into the Glaucocystidese and 

 the Archiplastideee (G. S. W. '04). It is probable, 

 however, that this Alga, notwithstanding its 

 brilliant blue-green colour, may have to be 

 removed entirely from the Myxophyceae when 

 more is known concerning the details of its 

 cytology. 



The curious Alga, Porphyridium cruentum 

 (Ag.) Nag., has been recently investigated by 

 Brand ('08 A and B), who brings forward strong 

 evidence to show that it must be regarded as 



a rudimentary form of the Bangiacere, which has never got beyond the embryonic 



state. 



Excluding Glaucocystis the Myxophycea? are primarily divided into the 

 two natural groups of the Coccogonea? and Hormogonese. 



Order I. COCCOGONESE. Unicellular or colonial plants, usually consisting 

 of colonies of unicells surrounded by mucous investments. The cells vary 

 much in form and in their disposition. The mucous investment is often 

 structureless, but may be obviously lamellose. The normal method of 

 multiplication is by simple cell-division, the larger colonies dissociating 

 to form smaller ones. Rounded asexual gonidia are known to occur in some 

 genera and species. The group includes the lowest of the Myxophycea? 

 and contains therefore the most primitive of the Alga?. They occur free- 

 floating in bogs and lakes, as gelatinous masses on wet rocks, and more 

 rarely as epiphytes. 



Fam. Chroococcaceae. This is the principal family of the Coccogonere and includes 

 nearly all the unicellular and colonial Blue-green Algae. In one genus (Gloeocli&te Lagerh.) 

 the cells are epiphytic and dorsiventral, each cell being furnished with one or two bristles ; 

 but in all the other genera the cells or colonies are either free-floating or form a 

 gelatinous stratum. The cells vary much in shape in the different genera, and with few 



B 



Fig. 24. Glaucocystis Nostochinearum 

 Itzigsh. Three cells showing the nucleus 

 (n) and the differences between the 

 chromatophores (chr) of young and old 

 cells. A is a young cell, B an older one, 

 and (7 one which is still older, x 720 

 (after Hieronyn^s). 



