376 



BOTANY OF THE LIVING PLANT 



Myxophyceae (Cyanophyceae). 

 The Blue-green Algae are unicellular, or filamentous. They are 

 found living either in water, or on surfaces which are habitually moist. 



A common type is seen in Gloeocapsa, 

 where the oval or spherical cells have a 

 swollen cell-wall. This holds the cells 

 together after fission, in rounded colonies 

 which break up by disorganisation of 

 the wall. It is commonly found on the 

 inner surfaces of the glass of damp 

 greenhouses (Fig. 279). Oscillatoria is a 

 filamentous type, which is common on 

 damp walls and rocks. Its pale green 

 filaments show slow swinging move- 

 ments, hence the name (Fig. 279A). 

 They consist of disc-shaped cells, which 

 multiply by division. In some of the larger forms granules of 

 irregular form are found in the so-called central body, which react 

 to stains like chromatin and divide before cell-division takes place. 



Fig. 279. 



Gloeocapsa polydermatica. A, in pro- 

 cess of division ; B, to the left, shortly 

 after division ; C, a later stage. 

 ( x 540.) (From Strasburger.) 



Fig. 279A. 



A, Oscillatoria princeps : a terminal portion of a filament ; b, portions from the 

 middle of a filament, properly fixed and stained ; t, cells in division. ( x 1080.) 

 a, UsctUatona Froeiichii. ( x 540.) (From Strasburger.) 



The filaments, which are unattached, may break up at any point 

 into several shorter lengths ; but in other cases special cells (hetero- 

 cysts) occur at intervals in the filaments, which appear to determine 

 their brewing up into shorter lengths, as in Nostoc or Rivularia. 

 Some of these fission-Algae take part in the formation of Lichens : 

 thus Collema has Nostoc as its Algal constituent. Others, such as 



