46 



LICHENALES. 



[Thallogens. 



XXXI 



universally of a green colour, and either lie singly or in clusters beneath the cortical 



layer of the thallus, or break out in clus- 

 ters called soredia, or in cups called 

 cyphelia. 



Nothing can be more varied than the 

 appearance of Lichens. If the grey, and 

 yellow, and brown stains upon old walls, 

 ancient churches, and other buildings are 

 carefully examined, those appearances will 

 always be found to arise from minute 

 Lichens having taken possession of the 

 surface of the stones, to which they adhere, 

 drawing their food from the atmosphere ; 

 small shields are scattered over their sur- 

 tax •, sometimes roimd, but not unfrequentlv 

 like dark clefts or lines, giving the Lichen 

 the appearance of being covered with 

 broken letters. Others are found on trees 

 and pales, forming broad patches of various 

 colours, some being of the richest golden 

 yellow ; others spread upon the ground in plantations and heaths— these have usually a 

 much larger growth ; some again hang from the branches of venerable trees, which they 

 clothe with a Bhaggy beard of grey ; and, finally, a few start up upon the heath, grey and 

 deformed, but eventually fashioning themselves into tiny goblets, the border of which is 

 studded with crimson shields. According to Fries, Lichens " are types of Algals born in 

 the air, interrupted in their development by the deficiency of water, and stimulated into 

 forming a nucleus by light. No lichen is ever submersed (Verruearia subrnersa is an 

 exception); there is none of which the vegetation is not interrupted by the variable 

 metrical state of the atmosphere ; and, finally, none that ever develop in mines, 

 caverns, or places deprived of light. On this account, their shields are more rare in the 

 fissures of mountains, or in Bhady groves, than in places fully exposed to light. In wet 

 places, also, their shields are not produced ; for so long as they are under the influence 

 of water they are hardly distinguishable from Hydrophycse (forms of Algals) ; as, for 

 instance, CoUema, &c. But these plants, when exposed to the sun, do perfect their 

 shields, as is found by Nostoc lichenoides, foliaceum, eve, which, when dry, are ascer- 

 ! to be Collema limosum, flaccidum, &c, surcharged with water." By being 

 acquainted with this rule, the same author says, he has succeeded in discovering many 

 Swedish lichens with shields, which have for many years been constantly found sterile; 

 as Parmelia oonoplea, lanuginosa, gelida, &c. ; and he even asserts that he has suc- 

 ceeded artificially in inducing sterile Lichens to become fruitful, as Usnea jubata, and 

 others, Plant. Horn. 224. Lichens consist, according to EschweUer, of a medullary 

 .-in. a cortical layer of tissue, of which the former is imperfectly cellular or filamentous, 

 and bursts through the latter in the form of shields (apothecia), which contain a nucleus, 

 consisting of a Bocculent gelatinous substance, among which lie the cases of sporules. 

 Itcsc case-, nh-e.c) are transparent membranous tubes, either simple or composed 

 ol several placed end to end, which either lie free in the nucleus, or are themselves 

 contained m other membranous eases (asci). In the beginning Lichens are stated 

 to be in all cases developed in humidity, and to be, in fact, at that time, mere 

 I nycemorl onfervm; hut as Boon as the humidity diminishes, the under part dies, 

 and an inert leprous crust is formed, which ultimately becomes the basis of the 

 H< nee I.u hens consist oi two distinct sorts of tissue,— living cellules forming 



an 

 plant 



- every part of the living 

 stratum has been ascertained to become reproductive matter. See Fries, as above 

 quoted,and Meyer Uebardu Eniwkkehmg, Ac, der FUcktm. The investigations of the 

 latter are exceedingly interesting. By sowing Lichens, he arrived at some curious con- 

 elusions, the chief of which are, that, like other imperfect plants, they may owe their 

 origin either to an elementary, or a reproductive., generating power — the latter 

 '';■ ,'" development like the plant by which they are borne: that decomposed 

 able, and some inorganic, j matter, are equally capable of assuming organisation 

 under th e influence of water and l ight ; and that the pulverulent matter of Lichens is 



IhTSta^l VtSSTrf S? Shie ' d ° f Parmelia ""a«a i the green gonidia are the black dots beneath 



tt££xzs\ aairr and paiaphyses ; a a 



