729 



LICHEN. 



1 JICIIEN is the name for an extensive natural order of 

 ""V""* 1 Pj* nt "' m *h e ' ower scalp of the vegetable creation. 

 They appear generally in the form of crusts, covering 

 rocks and the bark of trees. In English, they are 

 known under the comprehensive denominations of roc/c- 

 mou and tret-mots ; but few of the species are distin- 

 guished by particular names. The dye-stuffs called 

 orchal and cudbear, are kinds of lichen ; and so are the 

 oak-lung* and gruund-lirertrort, which at different times 

 hare been in estimation as medicines, the former in pul- 

 monary complaints, and the latter for the bite of a mad 



By the older botanical writers, the lichens were class. 

 ed along with the frondoee musci. Our countryman, 

 Morison of Aberdeen, Professor of Botany at Oxford, 

 towards the end of the 1 7th century, was the first who 

 separated them. He formed them into a genus, under 

 the title of Mtaro-funsus, their leathery substance lead- 

 ing him to consider tfiem as allied to tfie fungi. Tour- 

 nefort, in th- Inttilutionrt Rei Herbaria, 1 700, first ap- 

 plied to them the general term Lichen ; but he made a 

 separate genus of those having a coralline shape, de- 

 scribing them along with certain fungous plants, such 

 a* clavarisf, under the title of Coralloides. Micheli la- 

 boured indefatigably in illustrating the lichens. In his 

 Nova Plamtantm Genera, 1729, they are divided into 

 no fewer than 38 flections, and nearly 300 species are 

 described, and not a few of them delineated. Dille- 

 niu, in his Hitioria Mtaconan, 1741, arranged them 

 under the name* of Usnea, Coralloides, and Lichen- 

 oide*, leaving the simple word licfirn to signify the of- 

 ficinal liverwort. The filamentous species were associ- 

 ated with the conferva?, under the first-mentioned title 

 of* Umea; the former being Usnetc arborese, and tin- 

 latter Umea* aquatic*. 



The justly celebrated Linnaeus employed himself 

 chiefly in investigating pha*nogamous plants, by means 

 of which he was best able to establish his Sexual Sys- 

 tem. I n the Alga-, he did little more than arrange and 

 adapt to his own views the plants described by Miche- 

 li, Dillenius, and others. He greatly reduced the num- 

 ber of species of lichens, on account, it is presumed, of 

 the vagueness of the descriptions given by preceding 

 writers, which did not enable him to construct re- 

 gularly the' compendious, but luminous specific cha- 

 racters in which he delighted. He comprehended the 

 whole under one great and heterogeneous genus, Li- 

 chen ; but he divided it into eight sections, distinguish- 

 ed by the general habit and appearance of the plants : 

 I . Crnstaceous with tubercles ; 2. cmstaceous with 

 hield ; 3. tiled ; 4. foliaceous ; 5. leathery ; 6. bear- 

 ing cup* ; 7. shrub-like ; and 8. filamentous. 



Since the time of Liniueus, great progress has been 

 made in the investigation of the lichens. The distin- 

 guished Hedwig, and the still more accurate Gaertner, 

 examined with care the mode of propagation of this 

 tribe of plants, a subject which hud hitherto been little 

 attended to. But the author who principally extended 

 our lM.t.itiir.il knowledge of the lichens, was Dr. Hoff- 

 man of Gottingen. M.-twct-n 178* and 1792, this la- 

 borious author published descriptions and figures of all 

 the known species, under the title of En-imeralio Li- 

 ckeiHtm.. He, At the game time, attempted their divi- 

 sion into natural genera, founded, like the sections of 

 IJnnsrus, on the general habit of the plants. He was 



VOl. III. FABT II. 



Lichen. 



succeeded in this department of botany by Dr. Erich 

 Acharius, whose works, it is remarked by Sir James *""V*' 

 Edward Smith, " form a new era in cryptogamic bo- Acharius. 

 tany, and will most likely prove the foundation of all 

 that can in future be done on the subject." If, there- 

 fore, the illustrious Linnaeus was deficient in his ac- 

 quaintance with the alga, it was reserved for another 

 eminent Swede to elucidate this difficult branch of the 

 science. 



After some account of the scructure of lichens, and 

 of the mode of fructification, or of propagation, in this 

 obscure tribe of plants the reader shall be presented 

 with a detailed view of the Acharian system. Several 

 new terms must unavoidably be used ; but they shall 

 be as sparingly employed as possible, and their mean- 

 ing carefull}' explained. A short account of the uses 

 of the lichens, in domestic or rural economy, in medi- 

 cine, and in the arts, will be subjoined. 



Lichens are produced on the hardest and most bar- 

 ren rocks, and at great elevations ; on old walls ; on 

 the trunks and branches of trees, whether the bark be 

 smooth or rugged ; and on the surface of the earth, par- 

 ticularly in moorish soils. They are found in all cli- 

 mates, and at all times of the year, being naturally fit- 

 ted to resist, not only heat and cold, but dryness and 

 wetness. They suffer more, however, from drought 

 than from humidity ; and in this country, like the mus- 

 ci. they appear to greatest advantage at the moist sea- 

 sons of the year. A few notices regarding their habi- 

 tats, will be more intelligible after the Acharian ar- 

 rangement has been explained. 



Structure of Lichens. 



These plants have no distinct and regular roots. Some structure of 

 species, such as the common ground-liverwort, have lichens, 

 small fibres issuing from the edge and under-surface 

 of the frond : others are immediately attached to their 

 place of growth, for example, to stones, as if by a sort 

 of cement. They are equally destitute of stems, and 

 also of leaves, properly so called. The part .most ian- 

 alogous to a leaf, and which constitutes the principal 

 body of the plant, is frequently termed the^ronrf : by Thallus, 01 

 Acharius, it is denominated the thattui. This thalhis is frond. 

 often merely a thin flat crustaceous expansion ; some-- 

 times, however, it is foliaceous and lobed ; again, it is 

 branched, and like a shrub in miniature ; in some cases 

 it seems to be only a pulpy or gelatinous mass ; and in . 

 others, little else than a sort of powdery matter. 



In the leaf-like, and in the branched .lichens, the 

 thallus is distinctly composed of two parts. (1.) The 

 exterior is commonly hard, cartilaginous, or crusta- 

 ceous, homogeneous, with scarcely any signs of organi- 

 zation in its texture, but abounding every where with 

 very minute granular bodies, the nature of ..which will 

 be afterwards explained. This is called the cortical 

 substance. It forms both the upper and under stratum 

 of the thallus, in most of the foliaceous lichens, being 

 wanting below however in some of these, and also in 

 the uniform crustaceous species ; in those which are 

 shrub-like, it surrounds the branches and ramulL In 

 the humid state, the parenchyma of this cortical sub- 

 stance is somewhat gelatinous ; and in many species it 

 consists, to the extent of half its weight, of mucilage- 



