736 



LICHEN. 



Lichen, riolaria. II. Homothalamce, containing four genera, 

 """"Y""""' Lichen, Peltidea, Baeomyces, and Endocarpon. III. 

 Hetirolhalarrue, containing six genera, Verrucaria, Ope- 

 grapha, Lecidea, Gyromum, Calicium, and Sphseropho- 

 ron. In this way, Wahlenberg confines the number of 

 genera to twelve ; but the limited scope of his work, 

 being the description of the plants of Lapland only, 

 may have prevented him from introducing some other 

 genera, which, had his subject led him to examine 

 them, he might otherwise have felt inclined to adopt. 

 On account of the highly respectable character of this 

 author, it deserves to be noticed, that, in the work just 

 named, he mentions that his scheme for the arrange- 

 ment of lichens was composed in 1801, and at that time 

 communicated to Acharius, evidently leaving the read- 

 er to infer, that this. eminent lichenologist had availed 

 himself, without due ackiiowledgmeut, of his commu- 

 nication. 



Habitats of Lichens. 



Rocks. The general distribution of lichens has already been 



slightly touched on. It may here be observed, that 

 . certain species show an attachment for particular kinds 

 of rocks, in the same way as the more perfect plants 

 evince a predilection for different varieties of soils. The 

 hardest masses of granite and gneiss on the Scottish 

 mountains are the favourite residence of Lecanora ge- 

 lida, Lecidea petraea, silacea, lapicida, sulphurea, and 

 atrovirens, Parmelia fahlunensis, Verrucaria glaucina, 

 Opegrapha petraea, and Gyrophora proboscidea. Le- 

 canora fusco-atra var. dendritica has been observed on 

 pure rock-crystal. The porphyry rocks are preferred 

 by Lecidea pustulata and confluens, Parmelia ciliaris 

 and furfuracea, and Gyrophora deusta. The mica-slate 

 rocks seem to be the choice of Cornicularia tristis and 

 exilis, Gyrophora polyphylla, and of the vai.frigida of 

 Lecanora tartarea, which often appears branched, from 

 its twisting about mosses and remains of jungermanniae: 

 the clay-slate, of Lecidea Dicksoni and cupularis, Leca- 

 nora decipiens, and Baeomyces rupestris. The clay- 

 stone porphyries and different varieties of trap-rocks 

 are the favourite habitats of numerous species, such as 

 Lecidea fusco-ater, Urceolaria scruposa and cinerea, 

 Lecanora tartarea, Parmelia saxatilis and caperata. 

 Sandstone, especially if near the sea, is generally se- 

 lected by Ramalina scopulorum : Lecanora parella and 

 atra are likewise very commonly found upon it. Lime- 

 stone is preferred by Lecidea immersa, Collema nigra, 

 Vermcaria muralis, Urceolaria calcarea,'and Thelotrema 

 exanthematica. All of the lichens now mentioned, 

 however, are occasionally to be found on rocks of very 

 different geognostic and mineralogical characters, their 

 growth being much influenced by the circumstances of 

 elevation and exposure. 



Trees. In like manner, it may be remarked, certain species 



seem attached to particular kinds of trees ; but the 

 same species grow on various sorts of trees, assuming 

 a somewhat different habit on each kind, and to a cer- 

 tain extent acquiring different qualities. Thus, of the 

 Variolaria communis of Acharius, we have four varie- 

 ties, indicated by the trivial names faginea, alnea, pi- 

 nea, and abielina, from their growing on the beech, 

 the alder, the pine, and the spruce. 



Other hi- The most naked heaths form the favourite habitation 



busts. O f numerous species of Cenomyce. Coarse moist clay 

 is preferred by some of the Peltideae, as P. venosa and 

 horizontalis. The more gelatinous lichens often sup- 



port themselves by means of decaying mosses, around Lichen, 

 which they form incrustations,, as may be seen in Col- N ""V"*"' 

 lema pulposum, t',-uax, and trerhelloides, and jn Let-i- 

 dea muscorum. Some lichens grow on stones' under 

 water, as Collema fluviatile, and C. flaccidum var. ft. 

 Several species of Rhizomorpha inhabit the galleries of 

 deep mines, such as those of Leadhills, particularly R. 

 spinosa (Clavaria hypoxylon of most English authors), 

 and R. dichotoma and subterranea. A few small spe- 

 cies take up their abode, parasitically, on the musci he- 

 patici, and even on other lichens ; thus, var. ft of Leci- 

 dea cinereo-fusca has been observed on jungermannias, 

 and Calicium stigonellum (Lichen gelasinatus of Wi- 

 thering) on the crust of Porina pertusa. 



Uses of Lichens. 



It now remains only to give sonic account of the uses Uses ef 

 of lichens. Here no assistance is to be derived from lichens, 

 the labours of Acharius, his writings being purely bo- 

 tanical. Linna;us, Hoffman, Georgi, Lightfoot, WJ, 

 thering, and others, make amends ; and the essays on 

 this subject by Watson, by Amoreux the younger, by 

 Willemet, Westring, and Proust, might afford materials 

 for a longer dissertation than would be suitable for this 

 place. In the course of treating of their uses, we shall 

 notice the few observations which appear to have been 

 made by chemists on the constituent parts of lichens. 



Lichens are of great utility in the general economy In the eco- 

 of nature, although their operation is slow and almost nom ) of >' 

 imperceptible. The largest oaks of the forest, and ture - 

 most ancient pear-trees of the orchard trees which en- 

 dure for centuries at length become " mossed with 

 age," and more frequently owe their destruction to the 

 sflent attacks of parasitical lichens, especially of the 

 larger branched kinds, than to the ravages of storms. 

 But it is not merely on the " monarchs of the wood" 

 that lichens exert their influence. Many species, as we 

 have just seen, vegetate upon the barest and hardest 

 rocks : these, by their decay, prepare a suitable nidus 

 for the smaller frondose mosses. The mosses, in their 

 turn, afford sufficient soil for rock plants of a larger 

 size, such as stone-crop, or sheep's-fescue ; and thus 

 the rocks at length become covered with herbage, or 

 even with shrubby and arboreous plants. In this way, 

 we may distinctly trace to the vegetation of the hum- 

 ble crustaceous lichen, the commencement of one means 

 of that gradual but never-ceasing disintegration or de- 

 cay, which is wearing down the densest and loftiest 

 pinnacles of the earth. Meantime, lichens tend to en- 

 liven and variegate rock scenery, by " bestowing tints 

 of a delicate pea-green and primrose, which (to use 

 the words of Ann Radcliffe) it is not necessary to be a 

 botanist to admire." 



Food to Animals. In the extreme northern countries in rural 

 of Europe, the branched coralline lichen (Cenomyce economy, 

 rangiferina,) is highly important in rural economy, Hcin-deer 

 as affording the principal food of the rein-deer ani- lichen, 

 mals in which consist the whole riches of the inhabit- 

 ants. In Lapland, as we learn from Linnaeus, plains 

 of several miles in extent are often completely covered 

 with this lichen ; and in places where no other plant 

 will even take root, this thrives and becomes luxuriant. 

 These dreary wastes these "terra; damnatae," as a na- 

 turalist of a lower latitude has styled them are the 

 Lapland fields and fertile pastures. On these the rein- 

 deer feed daring winter. By a kind provision of na- 

 ture, it happens that at this pinching season, when no 

 other vegetable is to be had, the lichen, buried under 



