732 



L I C H E 



l.ichcn. the occurrence of intermediate verrucous receptacles, 

 "V"*' in some genera, should seem to present an obstacle. In 

 the mean time we shall adopt the language, and plan of 

 description, of the work last mentioned; not convinced, 

 however, tliat it would not be better, in laying down 

 the generic characters, to notice in the first place the 

 Thallus, which forms the bulk of the lichen, and then 

 the Apothecia, which are small and subordinate parts, 

 although they afford convenient distinctive characters. 

 Acharius divides lichens into three great classes. 1. 

 Idiofhafami, in which the apothecia are different in sub- 

 stance and colour from the thallus ; 2. Ccenotkalami, in 

 which they are partly formed of the thallus ; and 3. Ho- 

 molhalami, in which they seem to consist wholly of a 

 production of the cortical and medullary substance of 

 the thallus. These three classes embrace forty-two 

 genera, the author having "considerably increased the 

 number subsequently to the publication of his Methodus 

 Lichenum. By way of appendix, a class of Athalami is 

 added, in which no apothecia appear, or have hitherto 

 been detected : This includes only one genus. 



short tube with a wide mouth), and covered with a 

 thin coloured membrane; within, somewhat gela- 

 tinous, and of simple texture. Thallus crusjaceous, 

 uniform. 



System of Acharius. 



CLASS I. IDIOTHALAMI. 



A. HoMOGENEI. 



Aeharian Genus 1. SPILOMA. Apothecia varying in shape, and co- 

 genera, loured ; swollen or tumid, without a membranaceous 

 Spiloma. border, being composed of naked gongyli heaped to- 

 gether. Thallus crustaceous, uniform or of one shape, 

 somewhat membranaceous, and scaly or powdery. 



This and the next genus are not so distinctly marked 

 as most of the others. The species of Spiloma are found 

 on the bark of trees, or on decayed wood, having 

 usually the appearance of a scattered dark-coloured 

 powder. 



Arthor.ia. 2. ARTHONIA. Apothecia generally inclining to round- 

 shaped ; flattish, without a membranaceous margin ; 

 covered with a thin black membrane; internally, 

 somewhat gelatinous, and of simple texture. Thallus 

 crustaceous, uniform, or membranaceous, and some- 

 times approaching to cartilaginous. 



Lichen lynceus, described and figured in Sowerby's 

 English Botany, t. 809, affords an example of this gerius. 



Solorina. 3. SOLORINA. Apothecia roundish, sessile, without a 

 border ; covered with a coloured membrane ; within, 

 subgelatinous, and containing vesicles. Thallus lea- 

 thery, leaf-like ; beneath, veined or marked with 

 fibrils. 



This genus includes merely two species, the Lichen 

 croceus and saccatus of Linnaeus and of English Botany, 

 which were formerly ranked under Peltidea by Acha- 

 rius in his Methodus. Solorina crocea occurs on some of 

 the Scottish mountains, where it was first observed 

 by Dr. Stuart of Luss ; it is at once distinguished by 

 the fine saffron colour of the under-side of the frond. 

 In S. saccata, the apothecia or shields frequently ap- 

 pear sunk in sockets ; but this is only when the plant 

 is past its prime. 



Gjralecta. 4. GYALECTA. Apothecia circular ; concave, immersed 

 in the thallus, but with raised edges formed by the 

 gemmiparous plates; urceolated (or resembling a 



The generic name is derived from the Greek 

 concave, in allusion to the shape of the apothecia. This 

 genus includes only four or five species ; one of which 

 is the remarkable Lichen excavatus observed by Thun- 

 berg on the rocks at the Cape of Good Hope. 



5. LECIDEA. Apothecia circular, sessile, covered with Lecttle* 

 a coloured membrane; bordered by a regularly equal 



disk ; within, of simple texture. Thallus varying ; 

 crustaceous, either uniform or figured ; rarely folia- 

 ceous, and cloth-like or cottony. 



This is an important genus, containing more than a 

 hundred species, arid embracing many of the small 

 crustaceous lichens which ornament the hardest rocks, 

 and which first begin to operate their disintegration. 

 The genus is divided into three sections: 1. Catillaria, 

 with the thallus crustaceous and uniform; 2. Lepidonia, 

 with the thallus crustaceous, figured, and somewhat 

 leaf-like; and 3. Crocynia, with the thallus figured, 

 and cloth-like or cottony. In the first section occur 

 Lichen immersus, which is found sunk on the surface 

 of our limestone rocks, and of the chalk-cliffs of Eng- 

 land ; the well-known and beautiful variety of Lichen 

 atrovirens, called L. geographicus, from its resemblance 

 to a coloured map, a plant which is found at the 

 highest elevations, and which terminates the vegeta- 

 tion on Chimborazo ; L. Dicksonii, named in honour 

 of Mr. Dickson of Covent Garden, and found by him 

 on the Scottish mountains ; and L. sanguinarius, re-" 

 markable for the bright red which the apothecia pre- 

 sent when cut with a knife, or which they ultimately 

 acquire when they spontaneously open. As examples 

 of the second section, may be mentioned L. canescens, 

 hiridus, and leucophteus of British authors. Of the 

 third section, the only species is L. gossypinusof Swartz, 

 found on the Blue Mountains of Jamaica. 



6. GYROPHOHA. Apolhccia circular, sessile, spirally Gyrophora. 

 plaited; with a border; covered with a coloured mem- 

 brane (black); within, of simple texture. Thallus 

 leaf-like, membranaceous, peltate, or supported by a 

 central stalk. 



Lichen polyphyllus, proboscideus, and pustulatus, of 

 Linnaeus and of English authors, afford examples of this 

 genus. 



7. CALYCIUM. Apothecia cup-shaped, with a stalk 

 (rarely sub-sessile), and surrounded by a border ; 

 filled with a powdery mass, which forms at first a 

 flattish and afterwards a somewhat globular disk. 

 Thallus crustaceous, uniform. 



This genus is divided into three sections : 1 . With 

 sub-sessile cups, Acolium; 2. Cups stipitate or support- 

 ed on stalks, and furnished with a border, Phacotium ; 

 and S. Cups stipitate, the disk sub-globular, almost in- 

 closing the border, Strongylium. In most of the spe- 

 cies the crust is extremely thin, and in some it is scarce- 

 ly perceptible. Several of those with stipitate cups 

 have, by different authors, been referred to the genera 

 Mucor and Trichia ; for instance, Calycium aciculare 

 of Acharius is the Trichia fulva of Withering. 



8. OPEORAPHA. Apolhccia of an oblong shape, ses- Opegrapha. 

 sile, covered with a coloured membrane (black); with 



a straitened disk, inclosed by a border ; within, of 



