266 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



detect the species to which it was due. Tulasne, who has 

 specially exaniiaed the luminosity of the Agaric of the olive, 

 has observed dead leaves in the south of France to be endowed 

 with the same property, without, however, being able to detect 

 the cause. Fabre, in a paper just published in Ann. d. Sc. 

 Nat., ascribes it to a temporary increase of oxydation. 



266. Beautiful, however, as the effect may be in these 

 instances, it is far excelled by the phosphorescent appearance 

 presented by Rhizomorphce in mines, the splendour of which 

 is described by Humboldt in the most glowing colours. Such 

 Hhizortiorphce are, I believe, always mere subterranean forms 

 of common Fungi, as is the case with R. subcortlcalis. 

 Decandolle long since explained their real nature ; but it is 

 very curious, if this be the case, that our common Polypori and 

 Xylaria, which give rise notoriously to such productions, are 

 not themselves luminous when perfectly developed. One or 

 two properties of Fungi remain still to be noticed. When 

 wounded they are said to heal like the flesh of animals. 

 Though Phsenogams in general are incapable of growth where 

 tannin is present, not only several Fungi, as Agaricus cepces- 

 tipes, and volvaceus, delight in what is called spent tan, but 

 which still retains some of its original principle ; but a species 

 of Fungus, or rather the mycelium of some unknown species, is 

 develoj)ed in wood constantly soaked with a strong solution of 

 tan. Some sjDecies of the genus Boletus exhibit a very singular 

 change of colour, from white or yellow to a more or less vivid 

 blue. Archdeacon Robinson has examined this phenomenon 

 attentively in different gases, and has arrived at the conclusion 

 that the change depends on an alteration of molecular ar- 

 rangement. 



267. Before entering upon the different forms presented by 

 perfect Fungi, it may be well to say a few words respecting 

 the multitudinous false species and genera which appear in 

 systematic works, in consequence of infantile or abnormal states 

 being considered as perfect. No Fungus, however curious its 

 external appearance may be, should be regarded as of generic 

 value unless fructification be present. This principle alone 

 will dispose of a multitude of supposed species ; but, inasmuch 



