MYXOPHYCOPHYTA 

 NOSTOCALES 



287 



* This order comprises the great majority of the Myxophyceae. 

 It consists of the filamentous forms, which are either simple or 

 branched. The threads occur singly or aggregated within a common 

 gelatinous envelope. In some genera there is no difference between 

 base and apex of the filament whereas in others there may be. 

 Fundamentally the order is divided into those genera which lack 

 heterocysts and those which possess them, the heterocysts being 

 either basal or intercalary. Reproduction commonly takes place by 

 means of hormogones, but in some genera of the Nostocaceae and 

 Rivulariaceae, akinetes or spores are also produced. 



OsciLLATORiACEAE : SpiruUna {spirula, a small coil). Fig. 166 



The trichomes have no proper sheath and are septate, although 

 the septa are frequendy very obscure. The trichomes are simple, 

 free Hving and coiled into a more or less characteristic spiral. They 

 occur in fresh water or on the soil, including that of salt marshes. 



B 



Fig. 166 SpiruUna. A, S. major 



( X 1070). Bj S. subsalsa ( x 1070). 



(After Carter.) 



fS 



m 



XTr^ 



M 





^ 



5^ 



W 



m 



^ 





Fig. 167 Oscillatoria. A, O. for- 



mosa (x6i3). B, O. corallinae 



( X 613). (After Carter.) 



* OSCILLATORIACEAE: Oscillatoria (oscillare, to swing). Fig. 167 



The trichomes are free living, smooth or constricted, straight or 

 arcuate, and often form tangled masses, the sheath to each trichoma 



