282 
PHARMACEUTICAL BOTANY 
the dyes orcein and litmus. Litmus is one of the best indicators in 
volumetric analysis. Cudbear, a purplish-red powder, used exten¬ 
sively for coloring pharmaceutical preparations in the form of tinc¬ 
ture, is prepared by treating species of Rocella, Lecanora or other 
lichens with ammonia water. Other lichens, such as Cetraria 
islandica, various species of Parmelia , Usnea and Alectoria, have 
been used in medicine because of demulcent principles which they 
contain. 
DIVISION II.—BRYOPHYTA 
Plants showing a beginning of definite alternation of genera¬ 
tions, i.e., gametophyte (sexual phase) alternating with sporophyte 
Fig. 151. Fig. 152. 
Fig. 151.—Section of thallus of Cetraria islandica through an apothecium. as, 
Asci, three of which contain ascospores. gon , Gonidia. The inner (central por¬ 
tion shows the mycelial threads of a fungus entangling the alga. (Sayre.) 
Fig. 152.—A liverwort (Lunularia). Below, portions of the thallus, showing 
the lunar-shaped cupules, with brood-buds, or gemmae. Above a single gemma, 
greatly magnified. (Gager.) 
(asexual phase of development) in their life history, the two phases 
being combined in one plant. The female sexual cell is always 
lodged in an archegonium (a multicellular female sexual organ). 
