330 MyxophycecB 



constriction between the cells, or the latter may even be separated 

 by a mucous layer. In rare instances the trichomes are spirally 

 twisted. 



Sheaths are not always present in this family, and when 

 present, they are of very varied character. In some genera, such 

 as Microcoleus and Phormidium, the sheath is always colourless, 

 transparent, and more or less evanescent, whereas in others, such 

 as Schizothrix and Plectonema, it is of greater firmness, generally 

 branched, and often lamellose. 



Slow, gliding or rotatory movements are exhibited by some 

 species of Oscillatoria, Phormidium, Arthrospira and Spindina. 



The family is subdivided into two groups : 



Sub-family I. Vaginariece. Several trichomes included within a 

 single sheath, which is frequently branched. 



Sub-family II. Lyngtyecx. Never more than one trichome within 

 a sheath. 



Sub-family I. VAGINARIE.E. 



This sub-family contains the most highly organised of those 

 filamentous blue-green Algse which do not possess heterocysts. 

 The most important feature of the group is the inclusion of two 

 or many trichomes within the same sheath. The sheaths often 

 exhibit more or less branching, and are of two distinct types. In 

 one type they are firm and lamellose, often brown, brownish-red, 

 or even blue in colour ; in the other type they are mucous and 

 hyaline. Those of the first type always become of a blue colour 

 on the addition of chlor-zinc-iodine, whereas those of the second 

 type very rarely become coloured by this treatment. 



A. Sheaths generally coloured ; trichomes loosely aggregated within the 

 sheath, not very numerous. 



* Sheaths firm, lamellose, hyaline or coloured; con- 

 taining few or many trichomes Xchizothrix. 



** Sheaths wide, hyaline or yellow-brown, diffluent ; 



containing very few trichomes Dasygloea. 



B. Sheaths always hyaline, not lamellose, containing a 



large number of trichomes Microcoleus. 



Genus Schizothrix Kiitz., 1843. [Indus. Inactis Klttz., 1843; 

 Hyplueothrix Kiitz., 1843 (in part).] The filaments of this genus are 

 variously agglomerated to form small cushion-like masses, erect 

 tufts, or a flat stratum, and occasionally they occur floating freely in 



