ON DR. H. A. WEDDELl's REMARKS. 19 



atmosphere (he says, *'rain-Tvater contributes at least an equal 

 part of their nutrition."). I observed that rain is necessarily in- 

 cluded in the idea of the atmosphere, and that this water presents 

 nearly all the nourishing matter. The Weddellian discovery is, 

 therefore, a mistake, and of no use. 



III. The author had said that it was certain that silicicolous 

 lichens never (jamais) occurred upon organic substrata. Now, on 

 my admonition, correcting himself in " Grevillea," he confesses 

 that he should have said, " never, or almost never." This, how- 

 ever, is by no means sufficient. Acharius and Fries, whom he says 

 that he consulted on this subject, teach nothing indeed in that res- 

 pect ; but then he might have seen in Schaerer that Lecidea geogra- 

 phica had been gathered upon Rhododendi'on, while Lecanora gib- 

 bosa was cited as lignicole in " Nyl. Scand.," p. 154. Lichens, 

 however, were not very diligently searched for till after the year 

 1 860, whence it follows that the more recent writings of the last 

 ten years ought chiefly to have been consulted. It would then 

 have been easily perceived that very many silicicolous lichens (and 

 especially those very species Lecanora gibbosa, Lecidea geographica, 

 and Lecidea contigua, which the celebrated Weddell has pointed 

 out as being solely silicicolous), are by no means of rare occurrence 

 also upon dead bark or old wood. And if this is not more fre- 

 quently observed at the present day, it evidently depends, as may 

 be beheved, upon the circumstance that those lichens have a slow 

 and very protracted growth, and that scarcely anywhere, at least in 

 Europe, are the trunks of trees preserved intact through a long 

 series of years, so as to present a suitably hard woody, or as if 

 lithoid substratum. For instance, Lecidea contigua is sometimes 

 observed upon old bark and wood in lands where such long remain 

 undestroyed. In alpine regions Lecidea geographica lignicole 

 (Rhododendricole) occurs in hundreds of specimens. These and 

 other species usually silicicole, are distributed by numerous 

 examples in published collections. All of this may not please 

 Dr. Weddell, for he had his o/;//Mon formed as to silicolious lichens, 

 and any opposite observations seem to him to be unfriendly (" like 

 an enemy"). 



IV. There it is repeated that I have indicated oxalate of lime 

 as characteristic of all lichens, and the hostile author cites " Nyl. 

 Syn.," p. 4, where the sole question is (which he carefully over- 

 looks) concerning this oxalate as distinguishing lichens from fungi, 

 that is with respect to the inferior lichens approaching to fungi ; 

 which I have explained in various commentaries, for amongst the 

 Friesian attacks the same thing has long ago appeared. 



V. I, indeed, formerly enumerated the few lichens of the Lux- 

 embourg garden in Paris (at that time in great part about to be 

 destroyed), with the sole intention that it might be seen what species 

 could grow in the midst of a very large city, and in a garden 

 favourably situated there, which has nothing comparable with the 

 extended vegetation occm-ring near a town, where rural features 



