NOSTOC 451 



CYANOPHYCE^: 



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 : these are 

 short pieces of filaments which escape freely into the 

 water ; after a period of movement these settle, form a 

 gelatinous sheath, and grow into a new Nostoc mass. 



Compare the above observations with those on 

 Oollema (see below) : it is to be noted that Nostoc and 



G G 2 



