Single floating imicell^ / 

 Plate-like 

 colonies 



/' Single attached 

 Regular spherical / unicell 



or cubical colonies ^' ^ 



/ Attached ^^^^ 

 / simple filament Aggregated 

 Irregular ^ / \ filaments 



spherical / 

 colonies^' 



/ / filaments with 



false branching 



/ 



/ 



/ 

 / 



/ 



' filaments 



with true branching 



FLOATING / ATTACHED 



in places where no other vegetation can exist, e.g. hot thermal 

 springs. Their presence in great abundance in the plankton often 

 colours the water and is responsible for the phenomenon known as 

 water bloom, which in some cases may result in the death of the fish. 

 Members of the group also form a large constituent of the soil algae 

 (see p. 379). The plants, besides being primitive, are very ancient 

 and some of the earliest plant fossils known belong to the class (cf. 

 p. 294). It would seem that very little evolution has taken place 

 within the group since they first appeared. Their age and constancy 

 of form, together with their modes of reproduction, are also re- 

 sponsible for the wide distribution of different species, so that there 

 is little or no endemism in the Myxophycean flora of any region. 



The class used to be subdivided into two orders, but with the 

 advent of better knowledge (Fritsch, 1945) it is now divided into 

 five orders: Chroococcales, Chamaesiphonales, Pleurocapsales, 

 Nostocales and Stigonematales. Of these it is possible that the 

 Nostocales may require further subdivision. For those wishing to 

 identify species, standard works are those of Geider (1932)3 and 

 Tilden (1910). 



Chroococcales 



This order comprises unicellular forms that are free living and 

 either living singly or united into colonies. Reproduction takes 

 place by means of cell division in one or more planes. 



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