Heterocysts 



17 



manner between the vegetative cells of the filament (fig. 11 G), or they 

 may be terminal (fig. 11 F and G). Sometimes they are seriate as in 

 some species of Tolypothrix, Calothricc, Nostoc, etc. As a rule, they are 

 a little larger than the vegetative cells, and in most cases stand out 

 conspicuously among the other cells of the filament. There is almost 



Fig. 11. Various Blue-green Algse showing different positions of heterocysts. A and B, portions 

 of two branched filaments of Nostochopsis Goetzei Schmidle, with stalked and sessile lateral 

 heterocysts. C, fragment of filament of Nostoc carneum Ag., showing intercalary heterocyst. 

 D and E, small portions of filaments of Nostoc antarctica W. & G. S. West, showing 

 seriate intercalary heterocysts. F, Cylindrospermum tropicum W. & G. S. West with 

 basal heterocyst and papillate spore. G, Cylindrospermum indentation G. S. West, with 

 basal heterocyst and smooth indented spore. In all the figures the pellucid heterocyets are 

 represented without shading. The hair-like appendages around the heterocyst in G are 

 slender bacteria radiating in the colourless mucilaginous envelope. A, B and F, x520; 

 CE, and G, x 500. 



a complete absence of pigment from the heterocysts, in consequence of 

 which they present a very pellucid appearance, although they are often 

 of a pale yellow-brown or yellow-green colour. The walls of fully-formed 



w. A. 2 



