194 



DE CANDOLLE S SYSTEM. 



191. Marclantiacea or Hepatica. Plants composed en- 

 tirely of cellular tissue, emitting roots from their under side, 

 and consisting of an axis, bordered by a membranous expan- 

 sion, which sometimes forms a broad lobed thallus. Repro- 

 ductive organs consisting of a peltate stalked receptacle, bear- 

 ing theca3 on its under surface ; or of sessile naked thecse, im- 

 mersed, or superficial. 



USES. Unknown. 



TYPICAL GENERA. Marchantia, Riccia. 



192. Lichenacea. or Lichenes. Perennial plants spreading 

 in the form of a lobed thallus. Reproductive matter of two 

 kinds : 1, sporules lying in membranous tubes, immersed in 

 shields ; 2, separated cellules of the medullary layer of the 

 thallus. 



USES. Several are bitter, and some have been used as 

 tonics ; as Variolaria faginea, and Parmelia parietina. Others 

 are nutritious, as Iceland Moss, Cetraria islandica. Roccella 

 tinctoria is Orchal, and Lecanora Perellus, Cudbear, used ex- 

 tensively by dyers. 



TYPICAL GENERA. Parmelia, Lecidea, Peltidea. 



328. Shields of Variolaria amara. 329. A portion of the thallus of the same plant. 

 330. A piece of the thallus of Sticta pulmonacea with lacunae and soredia. 331. 

 Thallus of the same, bearing shields. 332. Shield of Opegrapha scripta. 333. Thal- 

 lus of the same. 334. Shields young and old of Lecanora Perellus. 335. Shields of 

 Bseomyces rufus. 336. Part of thallus of Peltidea canina. 337. Section of a shield 

 oi hticta pulmonacea. 338. Podetia of Cenomyce coccinea. 339. Section of shield 

 ol Baeomyces rufus. 340. Shields of Endocarpon miniatum. 341. Thallus of the 

 same. Chiefly from Greville's Flora Edinensis. 



