CYANOPHYCE^ 



253 



classifying the genera and species, the thicker kind 

 being frequently lamellated. The sheaths are at first 

 colourless and transparent, and may remain so, but 

 more often they become coloured as described. The 



FIG. 80. a, Bivularia hospita ; b and c, hormogonia of Calotlirix pulvinata 

 highly magnified. (After Bornet and Thuret.) 



heterocysts are special cells situated at the base of 

 the trichome or intercalated in its course. They are 

 bright green or light yellow in colour, have very little 

 solid contents, and are commonly much larger than 



