940 XII. LICHENES. 



Tkibe IV. MABOHANTIE^. 



Frond or thallus irregular, -with emarginate divisions, and no median nerve. 



Archegonia and antheridia borne on the lower surface of a peltate pedicelled disk, 



arising in a notch of the thallus. Sporangium furnished with elaters, but with no 



columella. 



PRINCIPAL GENERA. 



Tkibe V. ANTHOCEREJB. 



Frond or thallus irregular, without median nerves. Archegonia and antheridia 

 dispersed over the thallus. Sporangium siliculose, 2-valved, furnished with a central 

 columella covered with elaters. 



PRINCIPAL GENERA. 



Anfhoceros. Nothotylus. 



Hepaticce differ from true Mosses in habit, in the calyptra brealjing at the top and sheathing the base 

 of the pedicels, and in the structure of their sporangium without operculum, and usually accompanied by 

 elaters. They are connected with Sphagna by their mode of germination, the form of the antheridia, 

 and the absence of a normal cap or calyptra; but SpTiagna are distinguished by their habit, the form of 

 their sporangium, which is always furnished with a columella that disappears at maturity, their dimor- 

 phous spores, &c. 



Most of the genera are cosmopolitan ; some prefer temperate or cold regions ; but Oottschea, Thysa- 

 nanthus, Polyotus, &c., are principally tropical ; Targionia is exclusively temperate ; Cymatodium grows 

 in the Antilles. Two-thirds of RiccienB have been observed in Europe. Most Anthocerece, as well as the 

 rest of the family, are dispersed over the world. Some Sepaticcs have a very strong peculiar odour, 

 confined to certain species, of which they are characteristic, and a somewhat acrid taste. The ancients 

 looked upon Marehantia polymoipka as a resolvent medicine, and employed it in diseases of the liver. 

 M. chenopoda has a similar reputation in tropical America. 



XII. LICHENES, Jussieu. 



Cellular perennial Acotyledons, growing on the ground, stones, hark, the leaves of 

 other plants, and even on other Lichens. Organs OP VEGETATION (thallus) polymorphous, 

 irregular, spreading or erect, varied in substance and colowr, Repeoductive ORGANS 

 of two sorts : (1) (apothecia), situated on the surface or margin, or imbedded in the 

 thallus, varied in form, and colour, composed of sporangia (theCEe) containing 2— oo 

 spores ; (2) spermogonia, formed of spherical conceptacles imbedded in the thallus near the 

 apothecia, lined with filaments (sterigmata), which bear corpuscules of an extreme 

 tenuity, transparent, polymorphous (spermatia), considered as analogues of the anthero- 

 zoids, but not endowed with motion. 



