712 SYSTEMATIC BOTANY. 



b. Sporangia arranged in or near tlie axils of 

 leaves or bracts, or immersed in their substance. 



1. Not enclosed in sporocarps. 



Sporangia sessile, without a calyptra . . Lycopodiacce. 289, 

 Sporangia sessile, with a calyptra . . Musci. 21)0. 

 Sporangia stalked, with a calyptra . . Musci. 290. 



2. Enclosed in sporocarps. 

 Vernation circinate. 



Spores not mixed with elaters. . . Marsileacece. 288. 

 Vernation not circinate. 

 Spores mixed with elaters . . . Hepadcacece. 291. 

 B. Leafless plants. 



Stem simple, or with whorled branches. 

 Fructification terminal, in club-shaped or 



cone-lii<e masses Equisetace<e. 287. 



Stem always branched in a whorled manner. 

 Fructification at the base of the branches . Characcce. 292. 

 2. With no distinct stem or axis. 



Ho true leaves, but forming a green thalloid 

 expansion Hepaticacece. 291. 



Sub-class II. Thallogence. 



Natural Order 293. Lichenes. — The Lichen Order. — Peren- 

 nial plants, composed of pai'enchymatous cells, arranged so as 

 to form a foliaccous, somewhat woody, scaly, crustaceous, or 

 leprous thallus ; living and fructifying in the air, and growing 

 on the bark of trees, or on old palings, walls, &c., or on stones, 

 or on the exposed surface of rocks; usually epiphytic, but 

 sometimes parasitic, and commonly presenting a dry, 

 shrivelled, more or less lifeless appearance. Reproduction either 

 vegetative by gonidia (see page 38.5); or by trno, fructification^ 

 consisting of 1. apothecia, which are either sessile or stalked, and 

 commonly of a rounded {fig. 819J, or linear form {fig. 818), 

 and composed of asci or thecce (figs. 820 and 821), enclosing 

 4, 8, 16, or numerous spores; 2. oi spermagonia containing s/>er- 

 watia (figs. 822 and 823); and 3. of rarely, pycnidia with 

 stylospores. (For detailed account of the fructification of 

 lichens, see pages 382 — 385.) 



Distribution, Sfc. — Lichens are distributed in all parts of the 

 world. The pulverulent species " are the first plants that 

 clothe the bare rocks of newly formed islands in the midst of the 

 ocean, foliaccous lichens follow these, and then Mosses and 

 Liverworts." They also form a considerable proportion of 

 the vegetation of the polar regions and of mountain-tops. 

 Examples: — Pulveraria, Opegrapha, Verrucaria, Endocarpon, 

 Ijccidca, Cladonia, Peltigcra, Usnea. According to Fee, there 

 are 2400 species. 



Propertii's and Uses. — Several lichens possess nutritive pro- 

 ])erties from containing amylaceous substances, such are also 

 (emollient and demulcent ; others contain bitter principles, 

 which render them tonic and astringent ; and several are 



