NOSTOC. 



[ 463 ] 



NOSTOC. 



Fig. 534. 



verrucosum. 



Filaments mul- 



seen, by the aid of the microscope, to consist 

 of short, straightish pieces, which, as first 

 observed by Vaucher, are endowed with the 

 power of moving slowly along in the direc- 

 tion 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, to 

 form two new ones (fig. 534). 

 This process is repeated se- 

 veral times, and the mass of 

 new filaments becomes con- 

 fused, until the development 

 of a greater quantity of the 

 gelatinous matter, when they 

 become more distinct. The 

 same process was observed 

 in another species, which ap- 

 peared to be N. commune i 

 and Thuret considers it likely division 

 that this mode of reproduction Magn.soodiams. 

 extends to the other species. 

 We find that the gelatinous fronds break up 

 when kept in water, and the colourless cells 

 become green. Nothing is known of the 

 import of the enlarged, brighter cells. 



The resemblance of the Nostocs to the 

 species of Collema (Lichens) has attracted 

 much attention, and some authors even as- 

 sert that they are only different forms of the 

 same plants. We do not place much reliance 

 on the statements of Itzigsohn, but the me- 

 moir of Sachs on this subject is deserving of 

 attention. 



The gelatinous fronds of the British spe- 

 cies of this genus are found on damp ground, 

 wet rocks, mosses, &c., and free or attached 

 to stones in fresh water. 



* Frond globose or subglobose. 



1. Nostoc minutissimum, Kiitzing. Frond 

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

 deep ajruginous green, densely entangled ; 

 periderm growing brown. Kiitzing, Tab. 

 Phyc. vol. ii. pi. 1. fig. 1. Kiitzing doubt- 

 fully refers to the terrestrial form of this, 

 Hassall's N. muscorum (Br. Fr. Algce, pi. 74. 

 fig. 4), which grows on calcareous rocks, and 

 among the mosses covering them. 



2. N. lichenoides, Vaucher. Fronds from 

 the size of a mustard-seed to that of a pea, 

 aggregated and heaped together ; filaments 

 equal, loosely entangled, aeruginous or oliva- 

 ceous ; periderm pellucid, colourless, firm. 



. vesicarium ; larger, soft, with a fuscous 



distinct periderm, mucous within, sometimes 

 hollow. Kiitzing, Tab. Phyc. vol. ii. pi. 2. 

 iv. N. vesicarium, Hassall, Br. Fr. Algce, 

 p. 290. Road-side near Perth. 



3. N. sphcericum, Vaucher. Frond the 

 size of a pea, firm, blackish aeruginous or 

 somewhat olive-coloured, soft within ; fila- 

 ments pale green, loosely entangled; peri- 

 derm firm, colourless or fuscescent, sub- 

 opaque. Vaucher, Hist, des Conferees, xvi. 

 fig. 2 ; Kiitzing, Tab. Phyc. vol. ii. pi. 3. ii.; 

 Hassall, Br. Fr. Alga, pi. 76. fig. 5. On 

 stones in mountain rivulets. Meneghini 

 states, that when dried and again moistened, 

 it emits a pleasant odour like violets. Has- 

 sall thinks it probably an immature form of 

 N.foliaceum. 



4. N. cceruleum, Lyngbye. Frond from 

 the size of a pea to that of a sloe (rarely 

 larger), very soft and slimy, pale aeruginous 

 blue ; filaments unequal, loosely entwined, 

 joints oblong-elliptical ; periderm colourless, 

 pellucid, soft. Lyngbye, Hydrophytol. t. 68; 

 Kiitzing, Tab. Phyc. vol. ii. pi. 3. iv. ; Has- 

 sall, Br. Fr. Algce, pi. 74. fig. 1; 75. fig. 10; 

 76. fig. 11. Attached to mosses in flowing 

 water or very moist places. 



5. IV. pruniforme, Agardh. 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. Berkeley, 

 Gleanings, t. 19. 2; Kiitzing, Tab. Phyc. 

 vol. ii. pi. 4. iv. ; Hassall, Br. Fr. Algae, 

 pi. 76. 3-4 ; Lyngbye, Hydroph. t. 68 A. 

 Fronds unattached, in freshwater pools or 

 rivulets. 



** Frond foliaceous, irregular, or vesicular. 



6. N.foliaceum, Agardh. Frond terres- 

 trial, membranous, erect, plaited, olive-green; 

 filaments slender, copious. Hassall, Br. Fr. 

 Algce, pi. 76. fig. 2. On clayey ground con- 

 stantly moistened by oozing water. 



7. N. commune, Vaucher (fig. 532 & PI. 4. 

 fig.7). Frond terrestrial, gelatinous, subcoria- 

 ceous, olivaceous or obscurely green, irregu- 

 larly plaited; filaments nearly equal, flexuose, 

 colourless or green, loosely entangled, the 

 joints loosely conjoined, distant in one place, 

 geminate in others, subspherical, depressed, 

 marked with a central opaque spot ; peri- 

 derm hyaline, growing brown. Vaucher, 

 Hist, des Cow/, t. 16. fig. 1 ; Kiitzing, Tab. 

 Phyc. vol. ii. pi. 6. i.; Hassall, Br. Fr. Algce, 

 pi. 74. 2. Tremella terrestris, Dillwyn, Br. 

 Conferva, t. 10. fig. 14. Gravelly soils, 



