102 ROMANCE OF LOW LIFE AMONGST PLANTS. 



sudden appearance on garden paths, in masses occa- 

 sionally as large as a walnut, after a shower. Some 

 of the species are found in rivulets and ditches, some 

 on the ground, or on rocks, and some on walls or 

 glass. All are like little lumps of jelly, and when 

 examined microscopically are found to contain chains 

 of globose cells, variedly curved, immersed in the 

 gelatine (Fig. 19). By a singular coincidence this 



same kind of struc- 



^aripaCfl^^<x,^o O n ture is found in the 



o^;4>*#%o%::SoO^ thaHus of the gela- 



oo^'^f.h^yXSSt I tinous lichens, of the 

 ^%S%J^^oOl^, § group Co/Zemacec,. 



ooo O ^ c?^oq8:^cooo«fio" theorists who have 



contended that the 



Fig. 19.— Cells of Nostoc. 



alga is only an 

 early and imperfect condition of the lichen, and we 

 are reminded of certain experiments, in which it is 

 assumed that, by inoculation of the gelatinous mass 

 of the Nostoc, the Collema has been produced, artifici- 

 ally, with the true fructification of a lichen. Probably 

 something of this kind first suggested, or gave counte- 

 nance to, the theory, elsewhere alluded to, of the dual 

 nature of lichens. 



Normally the trichomes, or chains of subglobose 

 cells, in Nostoc have cither terminal or intermediary 

 cells, of a different colour and slightly different size, 

 which are termed heterocysts, but their function is 

 somewhat obscure. New plants are originated from 

 fragments of the trichomes, which are called hormo- 

 gofies. The mucilage of old plants becomes softened, 



