CRYPTOGAMIA ALG.E. 265 



constituent elements on being touched ; but, on the con- 

 trary, it lifts up in small pieces, for the filaments are 

 felted together, and form a compact though gelatinous 

 membrane. They are radiating, short, and so very slen- 

 der, that, under a considerable magnifier, they seem not 

 thicker than a hair, and present no appearance of striae. 

 They are well represented by VAUCHER. Oscillatoria 

 tennis of Dr GREVTLLE is a different species. 



3. O. oohracea, filaments simple, very slender, lying in a thick 

 cloud-like ochraceous stratum GREV. Fl. Edin. 304. Conferva 

 ochracea, DILLW. Syji. 59. t. 62. 



Hob. In small and rather deep pools at the sides of bogs, 

 frequent. 



This species covers the bottom of the pool with a thick light 

 ochre-coloured stratum, and throws up through the water 

 flocculent and waved masses, mimicking the heavy clouds 

 of our sky ; and it may be as transient, for a slight agita- 

 tion dissolves the brittle fabric, and diffuses it in muddy 

 fragments through the water. 



4. O. limosa, blackish-green, soft ; filaments straight and even, 

 very slender, rigid, without transverse striae, radiating round the 

 margins, but in the centre felted into a soft mass. HOOK. Scot. 

 ii. 79. Conferva limosa, DILLW. Syn. 38. t. 20. 



Hab. On damp walls, near their base, in Berwick, and on 

 the muddy edges of ditches. 



On damp walls this forms an irregular blackish-green spot, 

 and to discover its true form and appearance, it is neces- 

 sary to place a piece on a plate covered with water, where, 

 though apparently a shapeless mass, it will, in the space 

 of a night, shoot out an immense number of short filaments 

 radiating from the circumference, and forming a fine and 

 not inelegant fringe. I have seen this fringe completed 

 in less than an hour. The filaments are straight, pellucid, 

 and crystalline, but I could not discover any striae, per- 

 haps from the weakness of my magnifiers. 



The green scum which floats on the surface of stagnant pools 

 and drains in spring is not a species of this genus, but is 

 formed by a congeries of very minute globules, cohering 

 together from close apposition, and not through the me- 

 dium of any membrane or glutinous matter. 



YOL. II. M 



