Thallogexs.] LICHENALES. 4 7 



that which is subject to this kind of indefinite propagation, while the spores lying in 

 the sliields are the only part that will really multiply the species. He fiu'ther says, that 

 he has ascertained, by means of experiments from seed, that supposed species and even 

 some genera of Acharius, are all forms of the same ; as, for instance, Lecanora cerina, 

 Lecidea luteo-alba, and others, of the common Parmeha parietina. 



The distinction between Lichens and Fmigals has already been fully explained 

 by Mr. Berkeley (p. 30). It is, therefore, only necessary, in this place, to give a few 

 details concernuig the geographical distribution and uses of the order, or cluster 

 of orders, which Botanists combine imder the name of Lichens. 



Pulverulent Lichens are the first plants that clothe the bare rocks of newly-formed 

 islands in the midst of the ocean, foUaceous Lichens follow these, and then IMosses and 

 Liverworts. {D'Urville, Ann. Sc. 6. 54:.) They are found upon trees, rocks, stones, 

 bricks, pales, and similar places ; and the same species seem to be found in many 

 different parts of the world : thus, the Lichens of North America differ little from those 

 of Euroj^. They are not met with on decaying matter, where they give way to fungi ; 

 but they often occupy the surface of h-sing plants, especially theii* bark. In the tropics 

 they lay hold of evergreen leaves. Their chosen climate is one that is temperate and 

 moist ; aspects to the north or west are also their favoiu'ite resort, for they shun the 

 rays of the noon-day sim. No place seems to be a more constant haunt than the sur- 

 face of sand-stone rocks, and buildings, in cool and moist comatries. They are met 

 with, in one place or other, from the equator to the pole, and from the sea-shore to the 

 Umits of eternal snow. The finest species are found near the equator ; the most 

 imperfect, such as the crustaceous genera, which can hardly be distinguished from the 

 rocks they grow upon, are chiefly observed on mountain-tops, and near the pole. The 

 Idiothalami are most abundant in tropical America. 



Lichens liaA'e been remarked by De Candolle to possess two distinct classes of cha- 

 racters, the one rendermg them fit for bemg employed as dyes after maceration in 

 urine, the other making them nutritive and medicinally useful to man. Bracormot has 

 ascertained that oxalate of hme exists in great abmidance in Lichens, particularly in 

 those wliich are granular and crustaceous. The common Variolaria, which is found 

 upon almost every old beech-tree, contains rather more than twenty-nine per cent. 

 (Ed. P. J. 13. 194.) Lichens that grow on the summit of fir-trees have been formd 

 by John, of Berlin, to contam an uncommon proportion of oxide of iron, a cm-ious 

 illustration of the peculiar powers which various plants possess of separating the 

 inorganic matters presented to them in their food. (Ibid. 2. 394.) Of those used in 

 dyeing, the principal crustaceous Idnds are, Lecanora perella, the Orseille de terre, 

 or PereUe d'Auvergne of the French, Lecanora tartarea (or Cudbear), heematomma 

 and atra, Variolaria lactea, Urceolaria scruposa and ciuerea, Isidium Westringii, 

 Lepraria chlorina ; of the foliaceous species, Parmeha saxatilis, omphalodes, encausta, 

 conspersa, and parietina, Sticta pulmonacea, Solorina crocea, and G^Tophora deu?ta 

 and pustulata ; but the most important are Roccella tiuctoria and fusifoi-mis, the dye 

 of which makes litmus, and is largely used by manufacturers under the name of 

 Orchall, or Archill, or Orseille des Canaries ; there are other species capable of 

 being employed in a similar manner, as Usnea pHcata, Evernia prunasti'i, Alectoina 

 jubata, Ramalina scopulorum, and several Cenomyces. Dr. Robert Thomson finds the 

 common yellow pale Lichen (Paraieha parietma) to contain a pecuhar colouruig matter, 

 called Parietm, of a bright yellow. This is heightened by a drop of nitric, muriatic, or 

 sulphuric acid ; while mmute quantities of ammonia, or other alkalies, change it to a 

 rich red inclirung to purple. 



Agardh considers Lichens more neai'lyalhed to Fuugals than to Algals: he remarks, that 

 if Sphserias or Pezizas had a thallus, they would be Lichens, and that the same part is 

 all that determines such genera as Calycium, Verrucaria, or Opegrapha to be Lichens, 

 and not Fungi. He adds, that all the transitions from Algals to the state of Lichens, 

 which have been detected by modern inquu'ers, are mere degenerations into the form 

 of the Lichen tribe, and by no means into Lichens themselves. 



According to Fries, Lichens have the vegetation of Algals, and the fruit of Fungals. 

 {Systema, 52.) 



Fries refers Byssacese to Lichens with the followmg short character : — " Aerial, 

 perennial, constantly growing, with a filamentous texture ; consistuig of solid fibres 

 (either few or several glued together with a common bark), unchanged and permanent. 

 Fructification homogeneous, growing externally, and naked." Syst. Orb. Veg.'29l. Some 

 of these plants appear to be meteoric productions ; on one occasion they are said to have 

 suddenly overrim all the leaves of pines on the side next the \\ind m the neighbom'hood 

 of Dresden ; on another, on the 29th of Aug. 1830, to have in an mstant spread over 

 the sails and masts of a ship at Stockholm ; and Fries is disposed to consider the cobweb- 



