io8 



A TEXTBOOK OF THEORETICAL BOTANY 



f 



Surface of colony 



Sheath 



Heterocyst 



Fig. 89. — Nostoc sp. Section through part of a gelatinous 

 colony showing embedded filaments with heterocysts. 

 Each filament has an individual sheath of denser 

 mucilage. 



SPORES 



#■ 



Fig. 90. — Anabaena sp. Cells stained 

 with Methylene Blue showing 

 metachromatic granules. 



Fig. 91. — Nostoc linckia. Filament showin g '^'^'^^jl/o^^MJ^ • V 

 outer sheath, enlarged spores and inter- ■^>'-=»«*--^'"<^^'- 

 calary heterocyst. {After Pascher.) 



