There are no phenomena associated with fungi that are of greater interest than those which relate to luminosity. The fact that fungi under some conditions are luminous has long been known, since schoolboys in our juvenile days were in the habit of secreting fragments of rotten wood penetrated by mycelium, in order to exhibit their luminous properties in the dark, and thus astonish their more ignorant or incredulous fellows Rumphius noted its appearance in Amboyna, and Fries, in his Observations, gives the name of Thelephora phosphorea to a species of Corticium now known as Corticium cÆruleum, on account of its phosphorescence under certain conditions. The same species is the Auricularia phosphorea of Sowerby, but he makes no note of its phosphorescence. Luminosity in fungi “has been observed in various parts of the world, and where the species has been fully developed it has been generally a species of Agaricus which has yielded the phenomenon.”[A] One of the best-known species is the Agaricus olearius of the South of Europe, which was examined by Tulasne with especial view to its luminosity.[B] In his introductory remarks, he says that four species only of Agaricus that are luminous appear at present to be known. One of them, A. olearius, D. C., is indigenous to Central Europe; another, A. igneus, Rumph., comes from Amboyna; the third, A. noctileucus, LÉv., has been discovered at Manilla by Gaudichaud, in 1836; the last, A. Gardneri, Berk., is produced in the Brazilian province of Goyaz, upon dead leaves. As to the Dematium violaceum, Pers., the Himantia candida, Pers., cited once by Link, and the Thelephora cÆrulea, D. C. (Corticium cÆruleum, Fr.), Tulasne is of opinion that their phosphorescent properties are still problematical; at least no recent observation confirms them.

The phosphorescence of A. olearius, D. C., appears to have been first made known by De Candolle, but it seems that he was in error in stating that these phosphorescent properties manifest themselves only at the time of its decomposition. Fries, describing the Cladosporium umbrinum, which lives upon the Agaric of the olive-tree, expressed the opinion that the Agaric only owes its phosphorescence to the presence of the mould. This, however, Tulasne denies, for he writes, “I have had the opportunity of observing that the Agaric of the olive is really phosphorescent of itself, and that it is not indebted to any foreign production for the light it emits.” Like Delile, he considers that the fungus is only phosphorescent up to the time when it ceases to grow; thus the light which it projects, one might say, is a manifestation of its vegetation.

“It is an important fact,” writes Tulasne, “which I can confirm, and which it is important to insist upon, that the phosphorescence is not exclusively confined to the hymenial surface. Numerous observations made by me prove that the whole of the substance of the fungus participates very frequently, if not always, in the faculty of shining in the dark. Among the first Agarics which I examined, I found many, the stipe of which shed here and there a light as brilliant as the hymenium, and led me to think that it was due to the spores which had fallen on the surface of the stipe. Therefore, being in the dark, I scraped with my scalpel the luminous parts of the stipe, but it did not sensibly diminish their brightness; then I split the stipe, bruised it, divided it into small fragments, and I found that the whole of this mass, even in its deepest parts, enjoyed, in a similar degree to its superficies, the property of light. I found, besides, a phosphorescence quite as brilliant in all the cap, for, having split it vertically in the form of plates, I found that the trama, when bruised, threw out a light equal to that of their fructiferous surfaces, and there is really only the superior surface of the pileus, or its cuticle, which I have never seen luminous.

“As I have said, the Agaric of the olive-tree, which is itself very yellow, reflects a strong brilliant light, and remains endowed with this remarkable faculty whilst it grows, or, at least, while it appears to preserve an active life, and remains fresh. The phosphorescence is at first, and more ordinarily, recognizable at the surface of the hymenium. I have seen a great number of young fungi which were very phosphorescent in the gills, but not in any other part. In another case, and amongst more aged fungi, the hymenium of which had ceased to give light, the stipe, on the contrary, threw out a brilliant glare. Habitually, the phosphorescence is distributed in an unequal manner upon the stipe, and the same upon the gills. Although the stipe is luminous at its surface, it is not always necessarily so in its interior substance, if one bruises it, but this substance frequently becomes phosphorescent after contact with the air. Thus, I had irregularly split and slit a large stipe in its length, and I found the whole flesh obscure, whilst on the exterior were some luminous places. I roughly joined the lacerated parts, and the following evening, on observing them anew, I found them all flashing a bright light. At another time, I had with a scalpel split vertically many fungi in order to hasten their dessication; the evening of the same day, the surface of all these cuts was phosphorescent, but in many of these pieces of fungi the luminosity was limited to the cut surface which remained exposed to the air; the flesh beneath was unchanged.

“I have seen a stipe opened and lacerated irregularly, the whole of the flesh of which remained phosphorescent during three consecutive evenings, but the brightness diminished in intensity from the exterior to the interior, so that on the third day it did not issue from the inner part of the stipe. The phosphorescence of the gills is in no way modified at first by immersing the fungus in water; when they have been immersed they are as bright as in the air, but the fungi which I left immersed until the next evening lost all their phosphorescence, and communicated to the water an already sensible yellow tint; alcohol put upon the phosphorescent gills did not at once completely obliterate the light, but visibly enfeebled it. As to the spores, which are white, I have found many times very dense coats of them thrown down on porcelain plates, but I have never seen them phosphorescent.

“As to the observation made by Delile that the Agaric of the olive does not shine during the day when placed in total darkness, I think that it could not have been repeated. From what I have said of the phosphorescence of A. olearius, one naturally concludes that there does not exist any necessary relation between this phenomenon and the fructification of the fungus; the luminous brightness of the hymenium shows, says Delile, ‘the greater activity of the reproductive organs,’ but it is not in consequence of its reproductive functions, which may be judged only as an accessory phenomenon, the cause of which is independent of, and more general than these functions, since all the parts of the fungus, its entire substance, throws forth at one time, or at successive times, light. From these experiments Tulasne infers that the same agents, oxygen, water, and warmth, are perfectly necessary to the production of phosphorescence as much in living organized beings as in those which have ceased to live. In either case, the luminous phenomena accompany a chemical reaction which consists principally in a combination of the organized matter with the oxygen of the air; that is to say, in its combustion, and in the discharge of carbonic acid which thus shows itself.”

We have quoted at considerable length from these observations of Tulasne on the Agaric of the olive, as they serve very much to illustrate similar manifestations in other species, which doubtless resemble each other in their main features.

Mr. Gardner has graphically described his first acquaintance in Brazil with the phosphorescent species which now bears his name. It was encountered on a dark night of December, while passing through the streets of Villa de Natividate. Some boys were amusing themselves with some luminous object, which at first he supposed to be a kind of large fire-fly, but on making inquiry he found it to be a beautiful phosphorescent Agaric, which he was told grew abundantly in the neighbourhood on the decaying fronds of a dwarf palm. The whole plant gives out at night a bright light somewhat similar to that emitted by the larger fire-flies, having a pale greenish hue. From this circumstance, and from growing on a palm, it was called by the inhabitants “flor de coco.”[C]

The number of recognized phosphorescent species of Agaricus is not large, although two or three others may be enumerated in addition to those cited by Tulasne. Of these, Agaricus lampas, and some others, are found in Australia.[D] In addition to the Agaricus noctileucus, discovered by Gaudichaud, and the Agaricus igneus of Rumphius, found in Amboyna, Dr. Hooker speaks of the phenomenon as common in Sikkim, but he seems never to have been able to ascertain with what species it was associated.

Dr. Cuthbert Collingwood has communicated some further information relative to the luminosity of a species of Agaricus in Borneo (supposed to be A. Gardneri), in which he says, “The night being dark, the fungi could be very distinctly seen, though not at any great distance, shining with a soft pale greenish light. Here and there spots of much more intense light were visible, and these proved to be very young and minute specimens. The older specimens may more properly be described as possessing a greenish luminous glow, like the glow of the electric discharge, which, however, was quite sufficient to define its shape, and, when closely examined, the chief details of its form and appearance. The luminosity did not impart itself to the hand, and did not appear to be affected by the separation from the root on which it grew, at least not for some hours. I think it probable that the mycelium of this fungus is also luminous, for, upon turning up the ground in search of small luminous worms, minute spots of light were observed, which could not be referred to any particular object or body when brought to the light and examined, and were probably due to some minute portions of its mycelium.”[E] The same writer also adds, “Mr. Hugh Low has assured me that he saw the jungle all in a blaze of light (by which he could see to read) as, some years ago, he was riding across the island by the jungle road; and that this luminosity was produced by an Agaric.”

Similar experiences were detailed by Mr. James Drummond in a letter from Swan River, in which two species of Agaric are concerned. They grew on the stumps of trees, and had nothing remarkable in their appearance by day, but by night emitted a most curious light, such as the writer never saw described in any book. One species was found growing on the stump of a Banksia in Western Australia. The stump was at the time surrounded by water. It was on a dark night, when passing, that the curious light was first observed. When the fungus was laid on a newspaper, it emitted by night a phosphorescent light, enabling persons to read the words around it, and it continued to do so for several nights with gradually decreasing intensity as the plant dried up. In the other instance, which occurred some years after, the author, during one of his botanical trips, was struck by the appearance of a large Agaric, measuring sixteen inches in diameter, and weighing about five pounds. This specimen was hung up to dry in the sitting-room, and on passing through the apartment in the dark it was observed to give out the same remarkable light. The luminous property continued, though gradually diminishing, for four or five nights, when it ceased on the plant becoming dry. “We called some of the natives,” he adds, “and showed them this fungus when emitting light, and the poor creatures cried out ‘chinga,’ their name for a spirit, and seemed much afraid of it.”[F]

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.

Perhaps one of the most fetid of fungi is Thelephora palmata. Some specimens were on one occasion taken by Mr. Berkeley into his bedroom at Aboyne, when, after an hour or two, he was horrified at finding the scent far worse than that of any dissecting room. He was anxious to save the specimens, but the scent was so powerful that it was quite intolerable till he had wrapped them in twelve thick folds of the strongest brown paper. The scent of Thelephora fastidiosa is bad enough, but, like that of Coprinus picaceus, it is probably derived from the imbibition of the ordure on which it is developed. There needs no stronger evidence that the scent must not only be powerful, but unpleasant, when an artist is compelled, before a rough sketch is more than half finished, to throw it away, and seek relief in the open air. A great number of edible Agarics have the peculiar odour of fresh meal, but two species, Agaricus odorus and Agaricus fragrans, have a pleasant anise-like odour. In two or three species of tough Hydnum, there is a strong persistent odour somewhat like melilot or woodruffe, which does not pass away after the specimen has been dried for years. In some species of Marasmius, there is a decidedly strong odour of garlic, and in one species of Hygrophorus, such a resemblance to that of the larva of the goat moth, that it bears the name of Hygrophorus cossus. Most of the fleshy forms exhale a strong nitrous odour during decay, but the most powerful we remember to have experienced was developed by a very large specimen of Choiromyces meandriformis, a gigantic subterranean species of the truffle kind, and this specimen was four inches in diameter when found, and then partially decayed. It was a most peculiar, but strong and unpleasantly pungent nitrous odour, such as we never remember to have met with in any other substance. Peziza venosa is remarkable when fresh for a strong scent like that of aquafortis.

Of colour, fungi exhibit an almost endless variety, from white, through ochraceous, to all tints of brown until nearly black, or through sulphury yellow to reds of all shades, deepening into crimson, or passing by vinous tints into purplish black. These are the predominating gradations, but there are occasional blues and mineral greens, passing into olive, but no pure or chlorophyllous green. The nearest approach to the latter is found in the hymenium of some Boleti. Some of the Agarics exhibit bright colours, but the larger number of bright-coloured species occur in the genus Peziza. Nothing can be more elegant than the orange cups of Peziza aurantia, the glowing crimson of Peziza coccinea, the bright scarlet of Peziza rutilans, the snowy whiteness of Peziza nivea, the delicate yellow of Peziza theleboloides, or the velvety brown of Peziza repanda. Amongst Agarics, the most noble Agaricus muscarius, with its warty crimson pileus, is scarcely eclipsed by the continental orange Agaricus cÆsarius. The amethystine variety of Agaricus laccatus is so common and yet so attractive; whilst some forms and species Russula are gems of brilliant colouring. The golden tufts of more than one species of Clavaria are exceedingly attractive, and the delicate pink of immature Lycogala epidendrum is sure to command admiration. The minute forms which require the microscope, as much to exhibit their colour as their structure, are not wanting in rich and delicate tints, so that the colour-student would find much to charm him, and good practice for his pencil in these much despised examples of low life.

Amongst phenomena might be cursorily mentioned the peculiar sarcodioid mycelium of Myxogastres, the development of amoeboid forms from their spores, and the extraordinary rapidity of growth, as the well-known instance of the Reticularia which Schweinitz observed running over iron a few hours after it had been red hot. Mr. Berkeley has observed that the creamy mycelium of Lycogala will not revive after it has become dry for a few hours, though so active before.

M. J. Berkeley, “Introduction to Cryptogamic Botany,” p. 265.