Although the examples already cited are those of species of Agaric, luminosity is not by any means wholly confined to that genus. Mr. Worthington Smith has recorded his experiences of some specimens of the common Polyporus annosus which were found on some timbers in the Cardiff coal mines. He remarks that the colliers are well acquainted with phosphorescent fungi, and the men state that sufficient light is given “to see their hands by.” The specimens of Polyporus were so luminous that they could be seen in the dark at a distance of twenty yards. He observes further, that he has met with specimens of Polyporus sulfureus which were phosphorescent. Some of the fungi found in mines, which emit light familiar to the miners, belong to the incomplete genus Rhizomorpha, of which Humboldt amongst others gives a glowing account. Tulasne has also investigated this phenomenon in connection with the common Rhizomorpha subterranea, Pers. This species extends underneath the soil in long strings, in the neighbourhood of old tree stumps, those of the oak especially, which are becoming rotten, and upon these it is fixed by one of its branches. These are cylindrical, very flexible, branching, and clothed with a hard bark, encrusting and fragile, at first smooth and brown, becoming later very rough and black. The interior tissue, at first whitish, afterwards of a more or less deep brown colour, is formed of extremely long parallel filaments from .0035 to .015 mm. in diameter.
On the evening of the day when I received the specimens,[G] he writes, the temperature being about 22° Cent., all the young branches brightened with an uniform phosphoric light the whole of their length; it was the same with the surface of some of the older branches, the greater number of which were still brilliant in some parts, and only on their surface. I split and lacerated many of these twigs, but their internal substance remained dull. The next evening, on the contrary, this substance, having been exposed to contact with the air, exhibited at its surface the same brightness as the bark of the branches. I made this observation upon the old stalks as well as upon the young ones. Prolonged friction of the luminous surfaces reduced the brightness and dried them to a certain degree, but did not leave on the fingers any phosphorescent matter. These parts continued with the same luminous intensity after holding them in the mouth so as to moisten them with saliva; plunged into water, held to the flame of a candle so that the heat they acquired was very appreciable to the touch, they still emitted in the dark a feeble light; it was the same after being held in water heated to 30° C.; but putting them in water bearing a temperature of 55° C. extinguished them entirely. They are equally extinguished if held in the mouth until they catch the temperature; perhaps, still, it might be attributed less to the heat which is communicated to them than to the deficiency of sufficient oxygen, because I have seen some stalks, having become dull in the mouth, recover after a few instants a little of their phosphorescence. A young stalk which had been split lengthwise, and the internal substance of which was very phosphorescent, could imbibe olive oil many times and yet continue for a long time to give a feeble light. By preserving these Rhizomorphæ in an adequate state of humidity, I have been able for many evenings to renew the examination of their phosphorescence; the commencement of dessication, long before they really perish, deprives them of the faculty of giving light. Those which had been dried for more than a month, when plunged into water, commenced to vegetate anew and send forth numerous branches in a few days; but I could only discover phosphorescence at the surface of these new formations, or very rarely in their immediate neighbourhood, the mother stalks appearing to have lost by dessication their luminous properties, and did not recover them on being recalled to life. These observations prove that what Schmitz has written was not true, that all parts of these fungi were seldom phosphorescent.
The luminous phenomenon in question is without doubt more complicated than it appears, and the causes to which we attribute it are certainly powerfully modified by the general character of the objects in which they reside. Most of the German botanists give this explanation, others suppose that it forms at first or during its continuance a special matter, in which the luminous property resides; this matter, which is said to be mucilaginous in the luminous wood, appears to be in the Rhizomorpha only a kind of chemical combination between the membrane and some gummy substance which they contain. Notwithstanding this opinion, I am assured that all external mucous matter was completely absent from the Agaricus olearius, and I neither discovered it upon the branches of Rhizomorpha subterranea nor upon the dead leaves which I have seen phosphorescent; in all these objects the luminous surfaces were nothing else than their proper tissue.
It may be remarked here that the so-called species of Rhizomorpha are imperfect fungi, being entirely devoid of fructification, consisting in fact only of a vegetative system—a sort of compact mycelium—(probably of species of Xylaria) with some affinity to Sclerotium.
Recently an extraordinary instance of luminosity was recorded as occurring in our own country.[H] “A quantity of wood had been purchased in a neighbouring parish, which was dragged up a very steep hill to its destination. Amongst them was a log of larch or spruce, it is not quite certain which, 24 feet long and a foot in diameter. Some young friends happened to pass up the hill at night, and were surprised to find the road scattered with luminous patches, which, when more closely examined, proved to be portions of bark or little fragments of wood. Following the track, they came to a blaze of white light which was perfectly surprising. On examination, it appeared that the whole of the inside of the bark of the log was covered with a white byssoid mycelium of a peculiarly strong smell, but unfortunately in such a state that the perfect form could not be ascertained. This was luminous, but the light was by no means so bright as in those parts of the wood where the spawn had penetrated more deeply, and where it was so intense that the roughest treatment scarcely seemed to check it. If any attempt was made to rub off the luminous matter it only shone the more brightly, and when wrapped up in five folds of paper the light penetrated through all the folds on either side as brightly as if the specimen was exposed; when, again, the specimens were placed in the pocket, the pocket when opened was a mass of light. The luminosity had now been going on for three days. Unfortunately we did not see it ourselves till the third day, when it had, possibly from a change in the state of electricity, been somewhat impaired; but it was still most interesting, and we have merely recorded what we observed ourselves. It was almost possible to read the time on the face of a watch even in its less luminous condition. We do not for a moment suppose that the mycelium is essentially luminous, but are rather inclined to believe that a peculiar concurrence of climatic conditions is necessary for the production of the phenomenon, which is certainly one of great rarity. Observers as we have been of fungi in their native haunts for fifty years, it has never fallen to our lot to witness a similar case before, though Prof. Churchill Babington once sent us specimens of luminous wood, which had, however, lost their luminosity before they arrived. It should be observed that the parts of the wood which were most luminous were not only deeply penetrated by the more delicate parts of the mycelium, but were those which were most decomposed. It is probable, therefore, that this fact is an element in the case as well as the presence of fungoid matter.”
In all cases of phosphorescence recorded, the light emitted is described as of the same character, varying only in intensity. It answers well to the name applied to it, as it seems remarkably similar to the light emitted by some living insects and other animal organisms, as well as to that evolved, under favourable conditions, by dead animal matter—a pale bluish light, resembling that emitted by phosphorus as seen in a dark room.
Another phenomenon worthy of note is the change of colour which the bruised or cut surface of some fungi undergo. Most prominent amongst these are certain poisonous species of Boletus, such, for instance, as Boletus luridus, and some others, which, on being bruised, cut, or divided, exhibit an intense, and in some cases vivid, blue. At times this change is so instantaneous that before the two freshly-cut portions of a Boletus can be separated, it has already commenced, and proceeds rapidly till the depth of intensity has been gained. This blue colour is so universally confined to dangerous species that it is given as a caution that all species which exhibit a blue colour when cut or bruised, should on no account be eaten. The degree of intensity varies considerably according to the condition of the species. For example, Boletus cærulescens is sometimes only very slightly, if at all, tinged with blue when cut, though, as the name implies, the peculiar phenomenon is generally highly developed. It cannot be said that this change of colour has as yet been fully investigated. One writer some time since suggested, if he did not affirm, that the colour was due to the presence of aniline, others have contented themselves with the affirmation that it was a rapid oxidization and chemical change, consequent upon exposure of the surfaces to the air. Archdeacon Robinson examined this phenomenon in different gases, and arrived at the conclusion that the change depends on an alteration of molecular arrangement.[I]
One of the best of the edible species of Lactarius, known as Lactarius deliciosus, changes, wherever cut or bruised, to a dull livid green. This fungus is filled with an orange milky fluid, which becomes green on exposure to the air, and it is consequently the juice which oxidizes on exposure. Some varieties more than others of the cultivated mushroom become brownish on being cut, and a similar change we have observed, though not recorded, in other species.
The presence of a milky juice in certain fungi has been alluded to. This is by no means confined to the genus Lactarius, in which such juice is universal, sometimes white, sometimes yellow, and sometimes colourless. In Agarics, especially in the subgenus Mycena, the gills and stem are replete with a milky juice. Also in some species of Peziza, as for instance in Peziza succosa, B., sometimes found growing on the ground in gardens, and in Peziza saniosa, Schrad., also a terrestrial species, the same phenomenon occurs. To this might be added such species as Stereum spadiceum, Fr., and Stereum sanguinolentum, Fr., both of which become discoloured and bleeding when bruised, while Corticium lactescens distils a watery milk.
Fungi in general have not a good repute for pleasant odours, and yet it must be conceded that they are not by any means devoid of odour, sometimes peculiar, often strong, and occasionally very offensive. There is a peculiar odour common to a great many forms, which has come to be called a fungoid odour; it is the faint smell of a long-closed damp cellar, an odour of mouldiness and decay, which often arises from a process of eremocausis. But there are other, stronger, and equally distinct odours, which, when once inhaled, are never to be forgotten. Amongst these is the fetid odour of the common stinkhorn, which is intensified in the more beautiful and curious Clathrus. It is very probable that, after all, the odour of the Phallus would not be so unpleasant if it were not so strong. It is not difficult to imagine, when one encounters a slight sniff borne on a passing breeze, that there is the element of something not by any means unpleasant about the odour when so diluted; yet it must be confessed that when carried in a vasculum, in a close carriage, or railway car, or exposed in a close room, there is no scruple about pronouncing the odour intensely fetid. The experience of more than one artist, who has attempted the delineation of Clathrus from the life, is to the effect that the odour is unbearable even by an enthusiastic artist determined on making a sketch.