Fig. 171 Nostoc. A, portion of colony of N. linckia ( x 400). B, C, 

 germinating hormogones of N. puncttforme ( x 900). (After 



Geitler.) 



NOSTOCACEAE : Cylindrospermum (cylindro, cylindcT ;spermum, seed). 

 Fig. 172 

 A characteristic feature of this genus is the large spore which 

 develops next to the heterocyst at one or both ends of a filament. 

 The outer wall of the spore is often papillate. 



Fig 172 Cylindrospermum. A, C. ?7jajus ( x 680). B, C. stagnale 



( X 340). (After Geitler.) 



Stigonematales 



The members of this order, which is not large, form branched 

 threads, sometimes with a prostrate and erect portion. The branch- 

 ing is true and the threads may consist of more than one row of 

 cells. Characteristically the individual cells are apparendy con- 



291 



