M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 175 



Fungi are valueless from the tissue being destroyed by the ramify- 

 ing mycelium. Indeed, Fungi do not and cannot flourish on 

 growing and vigorous bark, but on diseased, dead, or decaying spots. 



Lichens obtain the greater portion of their pabulum from the 

 atmosphere, and only their mineral constituents from the matrix. 

 Hence they cover the trunks and branches of forest trees, without 

 apparent injury, aud many species habitally nourish on the hardest 

 granite. Fungi, on the other hand, obtain their chief support from 

 the decaying vegetable matter on which they flourish, gathering up 

 a large store of the nitrogenous results of putrefaction and decay, 

 and disintegrating the matrix on which they prey. 



Lichens, in their chemical composition, contain a large number 

 of substances which are wholly unknown amongst Fungi. Colorific 

 principles, such as obtain in the Orchella weeds, Orcellic, Cetraric, 

 Lecanoric, Tannic, and Gallic Acids, Lichenin, and even a peculiar 

 and characteristic odour, all of which cannot be attributed to the 

 gonidia they contain. 



Lichens contain but a small percentage of water as compared 

 with Fungi, so that in dessication they do not shrivel, collapse, or 

 perceptibly diminish in size, whereas Fungi shrivel up and collapse 

 so as scarcely to be recognised, becoming liable constantly to the 

 attack of insects, or, if damp, subject to the development of mould, 

 whilst Lichens may be preserved for years under like conditions 

 without fear of insect or mould. 



Lichens, when collected and cast aside without the slightest care 

 or precaution, do not exhibit the least tendency to putrefy, whilst 

 Fungi, with the utmost care in drying, can scarce be preserved from 

 unmistakable evidences of incipient putrefaction. 



Any one who has examined the thallus of such a Lichen as 

 Peltigera canma, and compared it with any known species of the 

 Discomycetes, must come to the conclusion that amongst them there 

 is no such structure to be found as that which prevails in the Lichen 

 thallus, altogether irrespective of gonidia. 



It is sometimes useful and instructive on doubtful points to con- 

 sult the instincts of the lower animals, and this course may be 

 adopted with advantage in the present instance. Amongst Coleop- 

 tera there is an entire family called the Mycetophagidce, many of 

 which live upon Fungi, and yet do not attack Lichens. There are 

 also some of the Bostrichidce and some species of Anobium very 

 fond of Fungi, but they do not attack Lichens. The insects which 



o 



