NOSTOC. 



[ 545 J 



NOSTOC. 



rows of cells (PI. 8. fig. 7) which increase 

 the length by repeated transverse sub- 

 Fig. 527. 



K"ostoc commune. 

 Natural size. 



division; here and there are larger cells 

 (, c) which appear brighter than the rest, 

 resembling the vesicular cells of the allied 

 genera. The filaments break up after a 

 time into short fragments, which by cell- 



Nostoc caDruleum. 

 Filaments. Magnified 200 diameters. 



division produce new filaments. The pelli- 

 cle of the frond bursts, allowing the gela- 

 tinous mass to escape, and the filaments to 

 spread abroad in the water ; 

 tnese consist of short straight- Fig. 529. 

 ish pieces, which move slowly 

 along in the direction of their 

 length; after a time they cease 

 to move, and a new gelatinous 

 envelope is formed around each 

 piece like a transparent sheath. 

 They soon become enlarged 

 considerably, and then divide 

 in the direction of the length of 

 the filament (fig. 529), which 

 becomes so disintegrated that 

 the filament forms a spiral, 

 by the increase of which 

 through further transverse 

 cell-division the mass be- 

 comes confused, until the de- 

 velopment of a greater quan- Ma 8 g l Sdiams. 

 tity of the gelatinous matter 

 makes the filaments more distinct. 



The British species of this genus are 



Nostoc 

 verrucosum. 

 Filaments mul- 

 tip 

 sut 



found on damp ground, wet rocks, mosses, 

 &c., and free or attached to stones, in 

 fresh water (PI. 8. fig. 7). They are very 

 numerous, and the following only can be 

 noticed. 



* Frond globose or subglobose. 



Nostoc minutissimum. Frond globose, 

 from 1-30 to 1-4'" ; filaments equal, deep 

 seruginous green, densely entangled j peri- 

 derm growing brown. 



N. lichenoides. Fronds from the size of 

 a mustard-seed to that of a pea, aggregated 

 and heaped together; filaments equal, 

 loosely entangled, seruginous or olivaceous ; 

 periderm pellucid, colourless, firm. 



(3. vesicarium; larger, soft, with a fuscous 

 distinct periderm, mucous within, some- 

 times hollow. 



N. sphcericum. Frond the size of a pea, 

 firm, blackish seruginous or somewhat olive- 

 coloured, soft within ; filaments pale green, 

 loosely entangled ; periderm firm, colourless 

 or fuscescent, subopaque. On stones in 

 mountain rivulets. Meneghini states that, 

 when dried and again moistened, it emits a 

 pleasant odour like violets. Hassall thinks 

 it probably an immature form of N.foli- 

 aceum. 



2V. cceruleum. Frond from the size of a 

 pea to that of a sloe, soft and slimy, pale 

 seruginous blue ; filaments unequal, loosely 

 entwined, joints oblong-elliptical ; periderm 

 colourless,' pellucid, soft. On mosses in 

 flowing water or very moist places. 



N. pruniforme. Frond the size of a large 

 round plum, deep aeruginous green, very 

 soft and watery within ; filaments unequal, 

 bright aeruginous green, loosely entangled, 

 joints subdepressed, dimidiate ; periderm 

 leathery, crystalline ; unattached, in fresh- 

 water pools or rivulets. 



** Frond foliaceotis, irregular, or vesicular. 



N. foliaceum. Frond terrestrial, mem- 

 branous, erect, plaited, olive-green; fila- 

 ments slender, copious. On clayey ground 

 constantly moistened by oozing water. 



N. commune (fig. 527, & PL 8. fig. 7). 

 Frond terrestrial, gelatinous, subcoriaceous, 

 greenish, irregularly plaited; filaments 

 nearly equal, flexuous, colourless or green, 

 loosely entangled, the joints loosely con- 

 joined, distant or geminate, subspherical, 

 depressed, with a central opaque spot ; 

 periderm hyaline, growing brown. Gravelly 

 soils, garden walks, rocks, barren pastures, 

 &c. ; very common in autumn and winter. 



