NOSTOCE^E. 227 



ft Trichoines homogenous, regular. 



1. Frond very small ; trichomes very 



compact 22. minutissimum. 



2. Frond attaining 2-10 mm. 



* Joints spherical, compressed . 23. gregarium. 

 ** Joints discoid, very compact . 24. edule. 



3. Fronds attaining the size of a nut 25. PRUNIFORME. 



VI. VERRUCOSA. Aquatic species. Fronds rounded or discoid, at first 

 full, then hollow, limited at the circumference by a firm and tough 

 periderm. Trichomes thin, very regular, spaced out and a little 

 flexuous at the centre, more compact, and very distorted at the peri- 

 phery. 



a. Fronds subglobose or warted. Mucilage 

 tolerably soft. Trichomes medium com- 

 pact, and often deprived of sheaths at 



the periphery 26. VERRUCOSUM. 



b. Fronds at first discoid or tongue-shaped, 

 a little ovoid, hard ; trichomes radiating 

 regularly from the centre to the circum- 

 ference and there forming a very dense 



layer 27. parmelioides. 



VII. ZETTERSTEDTIANA. Aquatic species. Fronds sphserical, hard, 

 tuberculose, divided into radiating separable 



lobes 28. Zetterstedtii. 



VIII. FLAGELLIFORMIA. Terrestrial species. Fronds forming thongs, 

 linear straight, and very long. 



Frond linear or setaceous, subdichotomous 

 trichomes longitudinally parallel . . 29. flagelliforme. 



I. INTRICATA. Species aquatic, fronds soft, gelatinous without 

 determinate form, often floating. 



Nostoc Linckia. (Roth.) Born % Thur. Notes Alg. p. 86, t. 28, 



/. 1-12. 



Fronds lobed, multipartite, free swimming, as large as n 

 walnut, lobes elongated and anastomosing, seruginous green, at 

 length becoming brownish. 



Trichomes flexuous, aggregated, joints short and close, 

 spherical, or sphaeiical compressed, sheaths uncoloured, very 

 refractive. Heterocysts slightly oblong. Spores subglobose or 

 oval. 



SIZE. Joints -0035 mm., heterocysts '005- '006 mm. diam., 

 spores (in form intricatwii) subglobose -0065 X *OU9 mm. 



Rivularia Linkia, Roth. Neue Beitr. p. 263. 



Nostoc confusum, Ag. Syst. Alg. p. 22. 



Monormia intricata, Berk. Glean, t. 18. Hass. Alg. 286, t. 

 75, f. 11. Ralfs. Ann. Nat. Hist. 1850, p. 326, t. 8, f. 1. 



Anabaena intricata, Kutz. Phyc. Germ. 171. Rabh. Alg, 

 Eur. ii., 183. 



Anabaena flos-aquce, Rabh. Alg. Sachs. No. 27. 



