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 



gon 



FIG. 151. PIG. 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). 



