2d. Where the elements are stratified, as in Parmelia, etc., the lichen is said to be heteromerous. In these there are three types:
a. Crustaceous lichens, the plant body is in the form of a thin incrustation on rocks, etc.
b. Foliaceous lichens, the plant body is leaf-like and lobed and more or less loosely attached by rhizoids: Parmelia, Peltigera, etc.
c. Fruticose lichens, the plant body is filamentous or band-like and branched, as in Usnea, Cladonia, etc.
Fig. 251a.
Rock lichen (Parmelia contigua).
[CHAPTER XXIII.]
LIVERWORTS (HEPATICÆ).
473. We come now to the study of representatives of another group of plants, a few of which we examined in studying the organs of assimilation and nutrition. I refer to what are called the liverworts. Two of these liverworts belonging to the genus riccia are illustrated in figs. [30], [252].