BOTANY TO MEDICINE. 263 



at least be sometimes useful even here. Had he, in addition to the 

 structure and economy of the more highly organized plants, traced 

 that of the descending series to the lowest verge of vegetable vita- 

 lity, and observed the distribution of the varied forms of both, such 

 circumstances would not be destitute of utility. He would have 

 become aware that the numerous species of lichens and fungi are 

 confined to peculiar media, upon which alone they would seem to 

 be capable of existing. The various primitive and secondary rocks 

 yield a resting place to particular species of the former tribe espe- 

 cially ; and so invariable is this attachment that the geological bo- 

 tanist, if I may be allowed the expression — seeing it is scarcely pos- 

 sible to separate, at least, an outline of the one science from an 

 intimate acquaintance with the other — the geological botanist will 

 often judge, by the hue of its surface clothed with a thin coating of 

 primeval vegetation, the composition of the rock which he is ap- 

 proaching. Thus, likewise, the greater number of the epiphytic 

 lichens, though probably subsisting solely upon the moisture con- 

 tained in the atmosphere, are not indiscriminately scattered upon 

 the stems of all tJie different species of trees in the same climate, 

 but vegetate exclusively upon those the outer surfaces of whose 

 barks afford them the necessary texture to which nature has adapted 

 their powers of adherence. The skilful landscape-painter knows 

 how to adapt his colours thus to the trunks of those trees he is de- 

 sirous of representing ; he sees that of the oak invariably differing 

 in the hue of its humble dependants, from that of the beech, the 

 elm from the willow, and so on of others. 



The fragments of the imported barks carry these minute and 

 long-neglected adherents to the living fabric which bore them, even 

 after being housed for years in the obscurity of our warehouses, 

 so little altered that the eye of the cryptogamic botanist is at no 

 loss to detect their very species. The memoir of Fee contains much 

 curious matter for speculation upon this subject ; and though his 

 researches have, perhaps, had more importance attached to them, by 

 some, than they actually deserve, it cannot be contested that these 

 natural indications of organic difference between the spurious and 

 true officinal barks, are entitled to more attention than the incredu- 

 lous, because often ignorant, inspector is willing to allow. 



