204 



TIIALLOPHYTES. 



to their substratum, at least on the under side, that they cannot be detached completely 

 from it without injury to the thallus (Fig. 184, A, B, C). The crustaceous Lichen-thallus 

 passes over, through various gradations, into that of the Foliaccous Lichens ; the latter 



Fig. 184.—^. B Graphis ele^ans, a crustaceous Lichen 

 growing on the bark of the holly ; A aatural size, B slightly 

 magnified ; C Pertusaria U'ul/eni, another crustaceous 

 Lichen (slightly magnified). 



Fig. 185.— a piece of the foliaceous thallus of PelH- 

 S-era horizontalis ; a the apothecia; r the rhizines 

 (natural size). 



Fig. 186. — Collema pjilposiaii, a gelatinous Lichen 

 (slightly magnified). 



forms flake -like expansions often curled, which can be completely detached from 

 the ground, stones, moss, bark, &c., which support them, since they are attached to it 

 only in places by a few organs of attachment, the Rhizines. The foliaceous thallus often 





Fig, iBy.—A Usnea harbata, a fruticose Lichen (natural size) ; B Sticta pjilmonacea, a foliaceous Lichen (natural size) 

 seen from beneath ; a apothecia, /"the attaching disc of A , by which the Lichen becomes attached to the bark of a tree. 



attains considerable dimensions, in the large species of Peltigera and Sticta as much as 

 a foot in diameter, and from | to i mm. in thickness, and then generally assumes a circular 

 form; at the growing margin it forms rounded indented lobes (Fig. 185 and Fig. 187, 5). 



