328 



Lichens are stated to be in all cases developed in humidity, and to be, in fact, at 

 that time, mere Phyceaj or Confervas ; but as soon as the humidity diminishes, 

 the under part dies, and an inert leprous crust is formed, which ultimately 

 becomes the basis of the plant. Hence Lichens consist of two distinct sorts of 

 tissue, — living cellules forming the vegetating part, and dead cellules the cohe- 

 sion of which is lost ; when separate, the former is Palmella botryoides, and 

 the latter Lepraria. Of these two sorts of matter, the leprous is incapable of 

 perpetuating the Lichen, while every part of the living stratum has been ascer- 

 tained to become reproductive matter. See Fries, as above quoted, and Meyer 

 Ueber die Entwickelung, fyc. der Flechten. The investigations of the latter 

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

 conclusions, the chief of which are, that, like other imperfect plants, they may 

 owe their origin either to an original elementary, or to a reproductive genera- 

 tion — {he latter by the creation of parts capable of developemen* in conformity 

 to the plant by which they are borne ; that decomposed vegetable, and some 

 inorganic, matter, are equally capable of assuming organization under the influ- 

 ence of water and light ; and that the pulverulent matter of Lichens is that 

 which is subject to this kind of indefinite propagation, while the sporules lying 

 in the shields are the only part that will really multiply the species- He fur- 

 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 com- 

 mon Parmelia parietina. As these remarks have not been, as far as I 

 know, contradicted, they may now be considered established facts. 



Agardh considers Lichens more nearly allied to Fungi than to Alga? : he 

 remarks, that if Sphrerias or Pezizas had a thallus, they would be Lichens, 

 and that the same part is all that determines such genera as Calycium, Verru- 

 caria, or Opegrapha to be Lichens, and not Fungi. He adds, that all the transi- 

 tions from Algae to the state of Lichens, which have been detected by modern 

 inquirers, are mere degenerations into the form of the Lichen tribe, and by no 

 mesns into Lichens themselves. 



With regard to the arrangement of the genera of Lichens, that of Acharius- 

 has been adopted by lichenologists of this country, and of most others ; but, 

 which is remarkable, not in Sweden ; and it seems probable, from the investi- 

 gations that have lately been instituted, that this celebrated s} 7 stem will, like 

 the more general one of Linnaeus, be wholly abandoned. In its room, every 

 writer upon Lichens has proposed a new one of his own ; Meyer, Eschweiler, 

 Wallroth, Agardh, Fries, Chevalier, Fee, have each brought forward methods 

 of arrangement, of which it may be said, without disparagement to any of 

 them, that it is impossible at present to say which will be eventually adopted. 



The only point to which it is further necessary to advert, is the separation of 

 the tribe called Hypoxyla from Lichens. In part, this is composed of Ope- 

 grapha and other Lichenoid, and of Sphaeria, and various Fungoid, genera : 

 its character is to discharge a sporuliferous pulp from the nucleus. But it 

 seems to be a prevalent opinion that this character is uncertain and unimpor- 

 tant, and consequently the supposed tribe will fall back in part into Lichens, 

 and in part into Fungi, from which it sprung. Dr. Greville, however, adheres 

 to the distinction. 



Geography. Pulverulent Lichens are the first plants that clothe the bare 

 rocks of newly-formed islands in the midst of the ocean ; foliaceous Lichens 

 follow these, and then Mosses and Hepaticee. D'Urville Ann. Sc. 6. 54. About 

 800 species are described by Acharius, the number of which is perhaps capable 

 of some reduction ; 200 are added by Fee, and great numbers are, no doubt, 

 still undiscovered. They are found upon trees, rocks, stones, bricks, pales, and 

 similar places ; and the same species seem to be found in many different parts 



