54 
S NOSTOC, Vauch. 
Thallus gelatinous or membranaceous, girt by a more or less firm 
periderm, definite, globose, or variously expanded. Trichomes flexu- 
Spores equal to the heterocysts, or a little larger, green, becoming 
bluish, olivaceous, or yellowish-brown.—Cooke, l.c. 
The Nostocs consist of a more or less firm jelly, in which beatae 
filaments are embedded, consisting of chains of small, somewna 
globose, simple cells. These filaments or trichomes, are usually sur- 
rounde 
r icho 
larger cells, or heterocysts, formerly regarded as spermatia, a 
differ in colour from the other cells of the trichome. Indivi : 
cells become heterocysts uninfluenced by any definite law at prese® 
demonstrated. Increase in the filaments is caused by division of the 
the heterocysts are detached and escape from th ilage, = 
the heterocysts re . These escaped fragments becre 
endowed with motion, similar to that observed in Oseillaria 
a 
; «es a 30 we 
are not present, on which account especially the determination ae 
certain.” 
Hab.: Burpengary, Thos. L. Bancroft. 
N. ceruleum, Lings. Cooke's British Freshwater Algz- i 
small, globose or subglobose (3 to 4 lines), fixed or free swiit. 
usually gregarious, blue or greenish-biue. Trichomes dissin 
unequal; joints of two forms, the one (young) elongated, se Size: 
larger, nearly spherical, sometimes filled with opaque granules. 
‘004-007 mm. ; heterocysts, mm. site 
Fig. 50 bis.: a, plant natural size; b, trichomes x 400; ¢ poe 
of trichome x 600.—Cooke, le 
Hab, : Still water, Victoria Park, W, J. Byram. Common in Europe. . 
