MYXOPHYCE^E (OR CYANOPHYCE^) 



(Blue-green Algae) 



. 



THE Myxophycea3 (which are also known as the Cyanophycese 1 and as 

 the Schizophycese 2 ) are the lowest and most primitive of Alga?, having in 

 their general organization a certain resemblance to the Bacteria. They 

 combine two outstanding features : first, the copious secretion of mucilage, 

 which often becomes very tough ; and secondly, the characteristic blue-green 

 colour of the cells. The latter feature may, however, be partially or wholly 

 masked owing to the presence of other pigments, either in the cells or in 

 coloured sheathing envelopes. Some are unicellular, some filamentous, and 

 many are colonial. They occur everywhere in damp and wet situations ; 

 and quite a large number exist in subaerial habitats. Owing to the bright 

 colours of the cells and sheaths, the Myxophycese furnish in moist climates 

 many of the richest tints of the landscape, and as they occur in profusion on 

 rocks, stones, and the trunks of trees, they sometimes impart a decided 

 character to the country. 



The Blue-green Algge are mostly freshwater and subaerial, although 

 a few inhabit brackish waters, and some are marine. Many forms exist 

 in quantity in the freshwater plankton, and a few in the plankton of the 

 warmer oceans. They also constitute the principal vegetation of hot 

 springs. 



1 The group-name ' Cyanophycea3 ' is a fairly good one, but it is being gradually superseded 

 by the name 'Myxophyceae,' which is perhaps a little better. Some 15 per cent, of the species 

 of this group are not of a blue-green colour at any period of their life, and about 30 per cent, of 

 the remainder have their cells so lodged within sheaths and gelatinous envelopes of a yellow, 

 orange, red, brown, or purple colour that they also do not appear blue-green in the mass. The 

 name ' Myxophyceas ' is now in general use except in the British Islands where it has been 

 thought more advisable to retain a ' colour name. ' 



2 The name ' Schizophyceae ' is a very inappropriate one, as 70 per cent, of the known species 

 are propagated by hormogones and spores, and do not multiply by fission. Moreover, in the 

 large group of the Hormogoneae cell-division is accompanied by the laying down of a new 

 transverse wall, and does not occur by 'fission' (consult p. 9). 



w. A. ] 



