LICHEN. 



licaris, Lin. (Ramalina scopnlorum, Ach.), which clothes 

 ^v"* many of our rocks near the sea, likewise belongs to it. 

 The generic name is derived from the Latin ranuilt, a 

 dead twig, the plants having been considered as resem- 

 bling, or perhaps as denoting, decayed branches. 



* 40. CoRKicL'LARiA. Apolhecia circular, obliquely pel- 

 tate ; at first, with scarcely a perceptible border, but 

 afterwards becoming dentate and reflexed ; wholly 

 formed of the thallus. T/iallus branched, slirub-like, 

 lender ; within, somewhat solid, of cottony sub- 

 stance, with a hard cartilaginous bark, rendering the 

 plant rigid and rather fragile. 



Lichen corniculatus of Flora Scotica (Cornicularia 

 tristis, Ach.), and L. hispidus (C. spadicea, Ach.), which 

 are found on rocks in the Highland districts, as well as 

 I., ix-hrolriu-us, which grows on the highest mountains 

 of Scotland, fiord examples of this genus. 



tans. 41. USSEA. Aptithfcin circular, peltate, very broad, 

 flat, without a border, but on the circumference some- 

 what ciliated, or. set with hair-like fibrils, (rarely al- 

 most naked ;) wholly formed of the thallus, and of 

 cottony substance within. Thallu* branched, fili- 

 form, with a tough thread-like fasciculus of little 

 ducts running along the centre, covered with a car- 

 tilagineo-crustaceous bark, rather brittle when dry. 



Lichen plicatus, floridus, and barbatus of Linnaeus, 

 are example*. These grow generally on old trees, and 

 in thick shady woods ; Lichen plicatus, indeed, is often 

 particularly distinguished by the name of 1'ree-moss. 



735 



I ,;,rri 



48. COLLCMA. An'.lhecin circular, immersed, sessile, 

 (rarely with a sort of pedicle), bordered, urceolate, 

 flat, entirely formed of the thallus. Tliallu* varying 

 in stupe, wholly of the same gelatinous kind of sub- 

 stance ; when dry, becoming hard and cartilagi- 

 nou*. 



The generic name is derived from *, gluten. 

 The specie* are pretty numerous ; they vary greatly in 

 aaptct, and are therefore distributed into no fewer than 

 aeven section*. I. PI 'cynl'num, with a crust-like tli.J- 

 K in Lichen niger, Lin. 2. E rhylihm, with the 

 thallii* imbricated, composed of small lobes, und round- 

 uh, as hi L cristatus, Lin. (follenia pulposum var. 

 Acb.) and in L. fascicularis. 8 Sci/tiniHtn, thai his fo- 

 liaceous, somewhat tiled, the lobes distinct, thick, tur- 

 gid ; as in L palmatus of Hudson. 4. Mallntium, fo- 

 liaceous, with the lobes rounded, and fibrils on the un- 

 der side ; a* in L, saturninus of Dickson, and L. Bur- 

 gessii of Lightfoot. 5. Lathagrium, foliaceous, with 

 the lobe* membranaceoux, broad, loose, of a blackish- 

 grern c- ' nir ; as in L. nigrescens, Lin. (L. vespertilio 

 of Lighboot). 6. Ijcpiopium, foliaceous, with the lobes 

 of very delicate diaphanous substance, generally glau- 

 cous ; a* hi L. tremella of English authors, (I'ollema 

 lacrrum, Ach.) 7- Polycliidtum, with the thallus very 

 finely branched and laciniated ; as in the minute and 

 elegant Lichen tenuissiinus of Dickson, and also in L. 

 rauscicula of die Mime author. 



(APPENDIX.) ATHALAMI. 



43. Lct-NAKtA. No apothecia. The gongyli (if such 

 they be) naked, loose, collected in little heaps. I'hal- 

 Ita cnistaceouK, powdery or leprous-like, uniform ; 

 in general/ composed almost entirely of gongyli or 

 propagujL 



VOL. III. PART II. 



Byssus candelaris of Linnaeus, or Lichen flavus of Lichen. 

 English authors, may exemplify this doubtful genus. y ~V 



Such is the arrangement adopted in the Licheno- 

 graphia Universalis of Acharius, with the additions 

 suggested by the author in the 12th volume of the 

 Linuenii Transactions. The greatest pains have evi- 

 dently been bestowed on the execution of the work. 

 As a proof of this, it may be noticed, that the generic 

 characters are all minutely and accurately illustrated 

 by figures, in as far at least as these characters depend 

 on the apothecia or shields. These figures are usually 

 magnified, and represent perpendicular, and sometimes 

 also horizontal sections, so as to afford the clearest pos- 

 sible explanation of the descriptions. But the generic 

 characters depend not only on the situation, shape, and 

 structure of the shields, but on the general habit and 

 form of the lichen. It has been objected, we believe, that 

 some of the characters of the genera are not sufficient- 

 ly obvious ; that, so far from being so, unpractised 

 eyes might find difficulty in detecting specific dif- 

 ferences where they ought to look for generic. To 

 those, however, who are somewhat accustomed to mi- 

 nute discrimination, this difficulty in a great measure 

 vanishes ; and from a single perfect specimen of any 

 species, the genus may generally without hesita- 

 tion be determined, while the similarity in external 

 habit very commonly leads to the association of the 

 other species of the same genus. In point of fact, too, 

 the principal generic characters of Acharius are taken 

 from the external parts of the plant, which are pretty 

 easily distinguished, although it necessarily happens 

 that these are often small, and must be examined with 

 a magnifying glass. The difficulty attending the mul- 

 tiplication of genera, it may be remarked, consists more 

 in appearance than in reality. Genera, it must be re- 

 membered, are necessarily artificial divisions, species 

 only being natural. The forty-three genera of Acha- 

 rius, may be considered as equivalent to as many sec- 

 tions of the overgrown genus Lichen of Liniurus ; and 

 thus the principal objection will resolve into the ad- 

 ditional tax on the memory of the botanist, who must 

 treasure up so many more generic names, some of them 

 not a little uncouth. While Acharius has increased the 

 number of genera, however, he has greatly reduced the 

 number of tpecies described by preceding writers. This 

 was to be expected, as the necessary result of a pain- 

 fully careful examination of the different appearance of 

 the same plants in their early and advanced stages, and 

 of the same species taken from different habifc.ts, from 

 a rock or from a tree, from a shady or an exposed situ- 

 ation. Colour, it is well known, is peculiarly liable to 

 variation, so that it cannot alone be depended on as a 

 character in describing natural bodies. But colours are 

 less liable to change in cryptogamic than in phaenoga- 

 mous plants, and they are therefore with propriety oc- 

 casionally noticed by Acharius ; still, however, when 

 colour is mentioned as a character by this cautious in- 

 vestigator, it is always in a subsidiary way, as indicated 

 by printing within parentheses. In the Licfienograpltia 

 Uniueriuiit, the synonymy is not nearly so ample as in 

 the Methtidus Lichenum ; but the name bestowed by 

 the discoverer, or by the author who first-described the 

 species, is commonly given ; and where species have 

 been represented in engravings, the best figures are re-; 

 ferred to. 



Dr. Wahlenberg of Stockholm, in his Flora iMppo^ Wahln. 

 nica, 1812, has also divided lichens into three classes. brg, 

 L Athalamie, containing two genera, Lepraria- and Va- 

 5 A 



