734 



LICHEN. 



Lichen. 



Acharian 

 genera. 



smaller receptacles, covered with a very delicate 

 transparent perithecium, punctured above with small 

 perforations ; nuclei subglobular, furnished with cells 

 and vesicles. 7'fiallut cartilagineo-membranaceous, 

 and somewhat crustaceous ; uniform. 



Of this genus, Lichen pertusus of British authors is 

 an example. 



Thelotre- 17. THELOTREMA. Apothecia wart-like, formed of the 

 thallus, hollowed, with a border ; each including a 

 single thalamium, or smaller receptacle, encircled by a 

 membranaceous perithecium, ultimately bursting a- 

 bove ; nucleus compressed ; within, of simple tex- 

 ture, and acquiring somewhat of a striated appear- 

 ance from the regular disposition of the gongyli. 

 Thallus cartilagineo-membranaceous, and somewhat 

 crustaceous; uniform. 



For illustration of this genus, Lichen inclusus, and 

 L. exanthematicus, of English Botany, may be referred 

 to. 



Pyrenula. 18. PYRENULA. Apothecia wart-like, formed of the 

 thallus, including a single subordinate receptacle or 

 thalamium, covered with a thick (black) cartilaginous 

 perithecium, which is prominent, and terminates in 

 a papilla ; nucleus globular, and furnished with cells. 

 Thallus crustaceous, or cartilagineo-membranaceous ; 

 uniform. 



This genus contains very few species, and is nearly 

 allied to Verrucaria and Porina. Lichen pertusus of 

 Thunberg is a Pyrenula ; but the pertusus of other au- 

 thors is a Porina. 



Variolaria. ip. VARIOLARIA. Apothecia wart-like, formed of the 

 thallus, (every where rough or scab-like ;) with an 

 indistinct border, including and concealing a com- 

 pressed gemmiparous plate, divided into cells, but 

 destitute of a perithecium. Thallus cartilagineo- 

 membranaceous, or crustaceous ; uniform. 



Lichen fagineus of Linnasus, which is pretty common 

 on the bark of our beech and hornbeam trees, is a vari- 

 ety of Variolaria communis of Acharius. Lichen lac- 

 teus, Lin. is likewise a Variolaria. 



Sagedia. 20. SAGEniA. Apothecia wart-like, formed of the thal- 

 lus, covered above with a coloured membrane; 

 marked with a disk-shaped depression, and conceal- 

 ing a gemmiparous plate, which is shaped like a nu- 

 cleus, immersed in the substance of the thallus, and 

 of simple texture within. Thallus crustaceous, uni- 

 form. 



Only six or seven species of this genus are known ; 

 they are small, and peculiar to hard rocks. One spe- 

 cies, S. rufescens, has been observed only on the sand- 

 stone rocks of England, where it was detected by Mr. 

 Turner. The name is derived from <rayv, a shield, the 

 apothecia greatly resembling small shields, which 

 might be said of several other genera. 



B. DISCOIDEI. 



Vrceoleria. 21. URCEOLARIA. Apothecia circular, with a border 

 formed by the thallus ; the gemmiparous plate co- 

 loured, forming a disk of the apothecium, having a 

 proper border, or being elevated on the circumfe- 

 rence, somewhat urceolate, and immersed in the sub- 

 6 



Lichen. 



stance of the thallus ; within, of a striated appearance, 

 and furnished with cells. Thallus crustaceous and 

 uniform; sometimes granulated or powdery /-charian 



' : genera. 



This genus is divided into two sections. 1 . Aspiste- 

 ria, in which the disk has no distinct border. To this 

 section belong Lichen lacustris of Withering; and L. 

 cinereus, Lin. a minute but common species, which of- 

 ten gives bare hard rocks a greyish appearance. 2. Am. 

 philomn, in which the border both of the apothecium 

 and the disk is distinctly raised. Of this division, Li- 

 chen scruposus, of Eng. Bot. and L. calcarius, Lin. (L. 

 cinerascens of Withering,) are examples. 



22. LECANORA. Aputhecia circular, thick, sessile, form- Lecanora. 

 ed of the thallus; gemmiparous plates coloured, form- 

 ing plano-convex disks of the apothecia ; encircled 

 by, but not in immediate connection with, elevated 

 unequal borders ofthe thallus ; within, striated, and 

 furnished with cells. TJtallus crustaceous, tartar- 

 like ; uniform, or somewhat lobed. 



This extensive genus, of which Acharius describes 

 above 130 species, is divided into three sections. 1. 

 Rinodina, with a uniform crustaceous thallus ; as in 

 Lichen ater, L. coarctatus, and L. Turneri, of Eng. Bot. 

 L. quadricolor and coccineus of Dickson, L. ventosus, 

 Lin.; and the well-known dye lichens, L. parellus' 

 from which litmus is prepared ; and L. tartareus, which 

 affords the cudbear ofthe west of Scotland. 2. Psoro- p tAT j: 

 mix, with a figured thallus, which is imbricated or squa- LXXV. 

 mous. Of thissection, the beautiful Lichen decipiens may Pg- *. b. 

 be mentioned as an example ; and likewise L. crassus of 

 Hudson, and L. candelarius of Linnaeus, with the shred- 

 ded frond of which " golden candles" are, in some coun- 

 tries, made for high festivals. 3. Placodia, with a flat 

 crustaceous thallus, stellated or lobed on the circumfe- 

 rence ; as in Lichen gelidus, or L. Hcclee of Flora Dani- 

 ca, L. flavicans of Withering, and the small but elegant 

 L. fulvus of Dickson. 



23. ROCCELLA. Apothecia circular, closely and wholly Roccelli 

 attached to the thallus ; gemmiparous- plates form- 

 ing plano-convex disks to the apothecia. encircled 

 with sessile borders formed by the thallus ; covering 

 globular but compressed masses, consisting of two 

 layers, the upper transparent and rather gelatinous, 

 the under blackish and compact, including nests of 

 naked gongyli. Thallus cartilaginous, and somewhat 

 leathery; round or thread-shaped, also flat and shrub- 

 like. 



To this genus belongs the celebrated dye lichen, L. PLATE 

 roccella, Lin. (Roccella tinctoria, Ach.) It grows on LXXV. 

 the sea rocks of Portland island, but is rare in England, fr'ig. 4. a. 

 The only other species of this limited genus hitherto 

 described, are the Lichen fuciformis, Lip. and L. fucoi- 

 des of Dickson, which occur on maritime rocks in the 

 south of England, and in the Channel islands. 



24. EVERNIA. Apothecia circular, sessile, edges raised, Evernia. 

 and slightly bent inwards ; gemmiparous plates form- 

 ing concave disks, surrounded by a border of the 

 thallus, which rises beyond them ; within, of simple 

 texture. Thallus branched or laciniated, cottony, or 

 woolly ; angular, sometimes compressed or flat. 



This genus includes thewell-known Lichen prunastri, 

 Lin. which grows abundantly on our trees ; and also 

 L. vulpinus, Lin. which is considered as poisonous, and 

 occurs sparingly on trees in this country. The generic 



