CYANOPHYCE.E. 



NOSTOC. 



This plant is to be found growing on turf, or Moss, 

 but not attached to it. It appears as irregular, more 

 or less flattened, olive-green masses, which are brittle 

 when dry, but soft and gelatinous when wetted. 



Mount a small piece, or a section of one, in water, 

 and it will be seen under a low power to consist of 

 numerous irregularly coiled filaments, embedded in a 

 gelatinous matrix. 



Under a high power each filament may be seen to 

 consist of series of small cells, with granular, blue-green 

 contents, which constitute the great proportion of the 

 filaments ; these series are interrupted here and there 

 by larger cells with firm, clearly-marked walls, and trans- 

 parent contents : these are the heterocysts. Observe 

 cases of cells which have recently undergone division. 

 Attempts may be made, by cultivating Nostoc in water, 

 to observe the separation and further development of 

 new masses by means of the hormogonia (cf. Goebel, 

 Outlines, Eng. Ed., page 22). 



Compare the above observations with those on 

 Collema (page 117) : it is to be noted that Nostoc and 

 Collema are frequently to be found closely associated 



