a Yellow Colouring Matter. 189 



ganic substances in the game manner as other plants. Viewed 

 in this light, the moistening and decomposing effect of a humid 

 atmosphere on the rocks on the sea-coast, may explain the 

 almost herbaceous appearance of some of the lichens which 

 may be observed in such situations. The subject, however, 

 of the nutrition of lichens, is in its infancy, and will require a 

 searching investigation. 



It has been already stated that, according to the opinion of 

 botanists (Hooker's English Flora), lichens derive no nourish- 

 ment from the rocks, stones, or trees, on which they grow. 

 The roots or fibres with which they are often supplied, it is 

 conceived, are only useful in fixing the plant to its place of 

 growth, its nutriment being derived from the air. One of the 

 most common of our lichens, the Pelt idea canina^ possesses 

 fibres on its under surface so closely resembling those of 

 shrubs, that one would be inclined to attribute to them similar 

 functions. The circumstance, as stated in chemical works, of 

 the absence of any considerable quantity of inorganic matter 

 in the composition of lichens, would appear to lend counte- 

 nance to the view, that gases constitute the only food of 

 lichens. But the fact of oxalate of lime having been obtained 

 from many lichens, seemed to call in question the validity of 

 the conclusion. The detection, also, of small portions of 

 bitartrate of potash and phosphate of lime in some lichens, 

 added still further evidence against the opinion of botanists. 

 So far as I am aware, no other substance of an inorganic 

 nature has been hitherto detected in lichens, except in such 

 minute proportion that it might have been derived, perhaps, 

 from extraneous sources. I was not, therefore, prepared to 

 expect the remarkable results which the analysis of the yellow 

 parmelia afforded. In one experiment, 50 grains, obtained 

 from mica-slate rocks at Dunoon, on the west coast of Scot- 

 land, when ignited, yielded 3.4 grains of inorganic matter; 

 and in another experiment, 40 grains, to which, as in the pre- 

 ceding trial, no earthy matter was attached, afforded, by burn- 

 ing, a residue of 2.7 grains. In a third experiment, 7 grains 

 of the carefully selected upper parts of fronds, which had never 

 been in contact with rock, and therefore were free from the 

 suspicion of having extraneous particles mixed with them, after 

 washing, as in the previous trials, yielded, by incineration, 



