324 



FAMILY NOSTOCHACEjE. 



Fig. 150. 



244. Nearly allied to the preceding is the little tribe of Nos- 

 tochacece ; which consists of distinctly- beaded filaments, lying in 

 firmly-gelatinous fronds of definite outline (Fig. 150). The filaments 

 are usually simple, though sometimes branched ; and are almost 

 always curved or twisted, often taking a spiral direction. The 

 masses of jelly in which they are imbedded are sometimes globular 

 or nearly so, and sometimes extend in more or less regular branches : 



they frequently attain a very con- 

 siderable size ; and as they occa- 

 sionally present themselves quite 

 suddenly (especially in the latter 

 part of autumn, on damp garden - 

 F lv ^v A walks), they have received the 



name of 'fallen stars.' They are 

 not always so suddenly produced, 

 however, as they appear to be ; 

 for they shrink up into mere 

 films in dry weather, and expand 

 again with the first shower. 

 There is strong evidence that 

 Nostocs are really the ' gonidia ' of 

 Collema and other Lichens, which, 

 when set free from the plants 

 which produced them, enter upon 

 an entirely new phase of exist- 

 ence. * They then multiply them- 

 selves, like the Oscillatoriacea?, by 

 the subdivision of their filaments, 

 the portions of which escape from 

 the gelatinous mass wherein they 

 were imbedded, and move slowly 

 through the water in the direc- 

 tion of their length : after a time 

 they cease to move, and a new gela- 

 tinous envelope is formed around 

 each piece, which then begins 

 not only to increase in length by the transverse subdivision 

 of its segments, but also to double itself by longitudinal fission, 

 so that each filament splits lengthways (as it were) into two 

 new ones. By the repetition of this process a mass of new filaments 

 is produced, the parts of which are at first confused, but afterwards 

 become more distinctly separated by the interposition of the gela- 

 tinous substance developed between them. Besides the ordinary 

 cells of the beaded filaments, two other kinds are occasionally ob- 

 servable ; namely, ' vesicular cells ' of larger size than the rest 

 (sometimes occurring at one end of the filaments, sometimes in the 



* See Hicks in "Quart. Journ. of Microsc. Science," Vol. i., N.S. 

 (1861), p. 90. 



Portion of gelatinous frond of 

 Nostoc. 



