386 INTRODUCTION TO CllYPTOGAMIC BOTANY. 



subject. The true Orchil weed is becoming scarce in the local- 

 ities which principally affordit, though there are many portions 

 of the world which yield either that or other valuable species. 

 When it is stated that specimens of Roccella fuciforonis were 

 exhibited at the Crystal Palace, from Ceylon, which were sup- 

 posed to be worth d&SSO per ton, and of Parmelia perlata 

 estimated at from ii'lQO to 6£'22.5, it may be imagined that 

 the subject is worth consideration.* 



427. fit was stated before, that the first traces of vegetation 

 on exposed rocks are due to minute Algse. This is true ac- 

 cording to the received notions of the affinities of these minute 

 bodies ; but as some of them are certainly the early stage of 

 Lichens, they must not be excluded. Lichens, indeed, in general 

 need no soil into which to strike their roots, or at whose ex- 

 pense they may live, but are capable of growing and being 

 propagated for indefinite periods where no other traces of 

 vegetation appear ; but some of the species, by their decay, 

 afford a fitting mould for the development of mosses, and 

 where these are once established Phsenogams soon follow. 

 This independence of soil is one cause, probably, of the very 

 extensive distribution as regards species ; for the genera and 

 species of Lichens are more completely cosmopolitan than 

 those of any other tribe of plants whatsoever. A large number 

 of species seem to occur in almost every part of the world, as, 

 for example, Usnea barhata, RaTnalitia calicaris, Parmelia 

 elegans, saxatilis, subfusca, Cladonia rangiferina and iiyxi- 

 data, Lecidea geographica, Pertusaria communis, Verru- 

 caria nitida, Thelotrem,a lepadinum, Biatora vernalis, 

 Graphis scripta, and GoUema tremelloides. These plants are 

 mentioned because they are well-known species, and also as 



* A great deal of interesting matter of various kinds relative to 

 Lichens, will be found in Dr. Lindsay's Popular History of British 

 Lichens. Reeves, 1856. See also Report in Gard. Chron., Aug. 4, 1855. 



t The Bev. Churchill Babington, who has a more intimate know- 

 ledge of Lichens in general, and more philosophical views on the sub- 

 ject than any British Botanist with whom I am acquainted, has kindly 

 drawn up for me far the greater part of the remarks relative to the 

 distribution of Lichens. 



