NOSTOC. 



281 



I. INTKICATA. Aquatic species. Fronds soft, gelati- 

 nous without determinate form, often floating. 



A. Trichomes forming irregular masses deprived 

 of the general mucilage. Circumvolutions of 

 trichomes distinct 



J?. Trichomes involved in mucilage more or less 

 abundant, loosely interwoven, joints of equal 

 diameter, rather distant ; spores subglobose. 



II. GELATINOSA. Fronds soft and gelatinous, ad- 

 herent, joints of trichomes cyliiidrically elongated 

 in the young filaments. Spores oblong large. 



A. Growing in watery or inundated places ; fronds 

 thick, deformed. 



B. Plant terrestrial. Frond plane, applied to the 

 ground by the inferior surface 



III. HUMIFUSA. Terrestrial species. Fronds at first 

 globose, then confluent, and forming gelatinous 

 cushions adhering to the substratum by their lower 

 face ; spores smooth, oval ; sheaths confluent. . 



Spores measuring 4x6 /z or more; mucilage toler- 

 ably firm ; trichomes olive ; spores oval. 



Mucilage soft, easily diffluent; trichomes aerugi- 

 nous green. 



IV. COMMUNIA. Terrestrial species, (sometimes in- 

 undated). Fronds at first globose, then becoming 

 tongue-shaped, plane, or irregular. Adult frond 

 suborbicular, folded, undulate, entire or lobed, often 

 perforated, and often expanded 



V. SPHAEKICA. Fronds globose or subglobose (often 

 becoming irregular when they grow large); limited 

 by a firm and resisting peridermic coating. 



^4. Terrestrial species. 



a. Fronds often large, firm, trichomes com- 

 pact, joints compressed spherical, rarely 

 cask-shaped ; close together, uniform. . 



b. Fronds soft, trichomes much spread out, of 

 unequal size, joints nearly spherical, sheaths 

 often colored, contrasting with the generally 

 uncolored mucilage 



c. Fronds very small, punctiform, not attain- 

 ing 1 mm diameter. Trichomes large, joints 

 cylindrical, a little constricted at the point of 

 junction ; spores globose smooth. . 



d. Trichomes fusiformly swollen between the 

 heterocysts. 



B. Aquatic species (color approaching to blue). 

 a. Trichomes dissimilar, unequal; joints of 

 two forms, the one (young) elongated, the 

 other large spherical often filled with opaque 

 granules . 



1. TKNUISSIMUM. 



2. COMMINUTUM. 



3. SPONGU.EFORME. 



4. ELL.IPSOSPORUM. 



5. MUSCORUM. 



6. HUMIFUSUM. 



I. (JALCICOLA. 



8. COMMUNE. 



9. SPHAERICUM. 



10. RUPESTRE. 



11. MACROSPORUM. 



12. SPH^ROIDES. 



13. CO3RULEUM. 



