NOSTOCE^. 



223 



B. Trichomes formed mostly of a 

 single row of cells. Sheath slen- 

 der. Aquatic plants looking like 

 Tolypothrix .... 



/'Sheaths enclosing several trichomes 



J Sheaths enclosing only a single trichome. 



Ramifications produced by the deviation of 



the trichome, which emerges from the side 



V. of the sheath ...... 



A. Ramifications usually geminate, pro- 



duced by a fold of the trichome 

 which ruptures outside of the 

 sheath, and gives birth to two 

 filaments given off at a right 

 angle. Heterocysts scattered 

 here and there in the trichome 

 without any evident relation to 

 the ramifications 



Sheath very broad, forming 

 a transparent layer around 

 the trichome 



7 Filaments agglutinated in 

 erect wick-like bundles 



B. Ramifications rarely geminate, often- 



times solitary, and originating at 

 a point where the continuity of 

 the trichome is interrupted by 

 heterocysts. One or several he- 

 terocysts placed directly above 

 each branchlet .... 



12 CALOTRICHE^ 4 



13 ( 



Filaments agglutinated by a 

 more or jless firm mucilage. 

 Frond usually with a well de- 

 fined outline .... 



Filaments free, growing in small 

 tufts, or forming a turf of 

 considerable extent 



Heterocysts scattered. Ramifications very 

 irregular, arising from a fold in the tri- 

 chome, in the form of a V, where originate 

 two geminate filaments, distinct at the base, 

 but at a certain height transformed, for the 

 greater part, into a single filament, composed 

 of a single row of cells. Frond hollow, but 

 hard, folded and looking like a little Rivu- 

 laria 



Heterocysts basal (placed at the base of the 

 principal filaments and branchlets). Ramifi- 

 cations produced by the transverse division 

 of the trichomes, the upper part of which 

 detaches itself and becomes a lateral branch- 

 let, while the lower part extending itself by 

 the side of its old tip makes a new extremity 

 similar to the first 



Haplosiphon. 

 Cystocoleus. 



A. B. 



Scytonema. 



Petalonema. 

 Symp liyosipkon. 



Tolypothrix. 



. 13 



Calothrix. 



Hormactis. 



14 



2 i 



