332 



are transparent membranous tubes, either simple or composed of several 

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

 contained in other membranous cases (a?ci). In the beginning Lichens are 

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

 time, mere Phycese or Confervee ; 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 

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

 and the latter Lepraria. Of these two sorts of matter, the leprous is inca- 

 pable of perpetuating the Lichen, while every part of the living stratum has 

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

 and Meyer Ueber die Entwickelung , 8fc., 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 im- 

 perfect plants, they may owe their origin either to an original elementary, 

 or to a reproductive generation — the latter by the creation of parts capable 

 of developement in conformity to the plant by which they are borne ; that 

 decomposed vegetable, and some inorganic, matter, are equally capable of 

 assuming organisation under the influence of water and light ; and that the 

 pulverulent matter of Lichens is that which is subject to this kind of inde- 

 finite propagation, while the sporules lying in the shields are the only part 

 that will really multiply the species. He further says, that he has ascer- 

 tained, 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 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 Algae : 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 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 means into Lichens themselves. 



With regard to the arrangement of the genera of Lichens, tliat of Acha- 

 rius 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 

 investigations that have lately been instituted, that this celebrated system 

 will, like the more general one of Linna-us, 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 for- 

 ward methods of arrangement, of which it may be said, without disparage- 

 ment 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 

 Opegrapha and other Lichenoid, and of Sphasria 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 unim- 

 portant, 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. 



Geogkapiiy. Pulverulent Lichens are the first plants that clothe the 

 bare rocks of newly-formed islands in the midst of the ocean, foliaceous 



