68 University of Calif arnia Publications in Botany [Vol. 8 



17. Phormidium Kuotz. 



Trichomes many celled, single witliin a sheath, simple, frequently 

 attenuate and uncinate at the apices; sheatli distinct, hyaline, some- 

 times mucous, more or less diffluent, in a few species obscure. 



Kuetzing, Phyc. Gen., 1843, p. 190. 



Kuetzing enumerated twenty-eight species under his genus Phor- 

 midinm, not designating any particular one as the type. Certain 

 species (about three) are not retained by Gomont, but most of them 

 are and there can be no question as to the main ideas of Kuetzing 

 which have been retained by Gomont. These are, first, the possession 

 of sheaths less firm than those of Lynghya, and second, the diffluence 

 and coalescing of these sheaths into a membrane or layer of jelly 

 enclosing a large number of filaments. In some species admitted to 

 the genus hy Gomont there is little if any trace of a sheath. These 

 species are approximate to Oscillatoria. During the period, or stages, 

 of hormogonial production, the hormogonia, or even whole trichomes, 

 escape from the sheaths and enclosing jelly. In this stage they are 

 exactly like the trichomes of Oscillatoria. 



The majority of the species of Phormidium are inhabitants of f resli 

 water, but a few occur also in brackish water, while a very few are 

 exclusively marine. 



Key to the Species. 



1. Trichomes distinctly torulose (Moniliformia) 2 



1. Trichomes rarely or scarcely torulose (Euphormidia) 3 



2. Trichomes attenuate at the apices, terminal cell acutely conical 



1. Ph. fragile (p 69) 



2. Trichomes not attenuate at the apices, terminal cell swollen, subspherical 



2. Ph. hormoides (p 69) 



3. Apices of trichomes neither attenuate nor capitate 3. Ph. ambiguum (p 70) 



3. Apices of trichomes both attenuate and capitate 4 



4. Trichomes slightly and abruptly tapering at the apices, terminal cell 



rounded, calyptrate 4. Ph. lucidum (p 71) 



4. Trichomes gradually tapering at the apices, terminal cell with depressed 

 conical calyptra 5. Ph. submembranaceum (p 71) 



Section 1. Moniliformia Gomont 



Trichomes distinctly torulose, even moniliform in some cases, 

 neither curved nor capitate at the apices. 



Gomont, Monogr. des Oscill., 1892, p. 159 (1893, p. 179, Kepr.). 



1. Ph. fragile (Menegh.) Gomont 



2. Ph. hormoides S. and G. 



