1911 Encyclopædia Britannica/Mushroom

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MUSHROOM.[1] There are few more useful, more easily recognized, or more delicious members of the vegetable kingdom than the common mushroom, known botanically as Agaricus campestris (or Psalliota campestris). It grows in short grass in the temperate regions of all parts of the world. Many edible fungi depend upon minute and often obscure botanical characters for their determination, and may readily be confounded with worthless or poisonous species; but that is not the case with the common mushroom, for, although several other species of Agaricus somewhat closely approach it in form and colour, yet the true mushroom, if sound and freshly gathered, may be distinguished from all other fungi with great ease. It almost invariably grows in rich, open, breezy pastures, in places where the grass is kept short by the grazing of horses, herds and flocks. Although this plant is popularly termed the “meadow mushroom,” it never as a rule grows in meadows. It never grows in wet boggy places, never in woods, or on or about stumps of trees. An exceptional specimen or an uncommon variety may sometimes be seen in the above-mentioned abnormal places, but the best, the true, and common variety of the table is the produce of short, upland, wind-swept pastures. A true mushroom is never large in size; its cap very seldom exceeds 4, at most 5 in. in diameter. The large examples measuring from 6 to 9 or more in. across the cap belong to Agaricus arvensis, called from its large size and coarse texture the horse mushroom, which grows in meadows and damp shady places, and though generally wholesome is coarse and sometimes indigestible. The mushroom usually grown in gardens or hot-beds, in cellars, sheds, &c., is a distinct variety known as Agaricus hortensis. On being cut or broken the flesh of a true mushroom remains white or nearly so, the flesh of the coarser horse mushroom changes to buff or sometimes to dark brown. To summarize the characters of a true mushroom—it grows only in pastures; it is of small size, dry, and with unchangeable flesh; the cap has a frill; the gills are free from the stem, the spores brown-black or deep purple-black in colour, and the stem solid or slightly pithy. When all these characters are taken together no other mushroom-like fungus—and nearly a thousand species grow in Britain—can be confounded with it.

The parts of a mushroom consist chiefly of stem and cap; the stem has a clothy ring round its middle, and the cap is furnished underneath with numerous radiating coloured gills. Fig. 1 (1) represents a section through an infant mushroom, (2) a mature example, and (3) a longitudinal section through a fully developed mushroom. The cap d, e is fleshy, firm and white within, never thin and watery; externally it is pale brown, dry, often slightly silky or floccose, never viscid. The cuticle of a mushroom readily peels away from the flesh beneath, as shown at f. The cap has a narrow dependent margin or frill, as shown at g, and in section at h; this dependent frill originates in the rupture of a delicate continuous wrapper, which in the infancy of the mushroom entirely wraps the young plant; it is shown in its continuous state at j, and at the moment of rupture at k. The gills underneath the cap l, m, n are at first white, then rose-coloured, at length brown-black. A point of great importance is to be noted in the attachment of the gills near the stem at o, p; the gills in the true mushroom are (as shown) usually more or less free from the stem, they never grow boldly against it or run down it; they may sometimes just touch the spot where the stem joins the bottom of the cap, but never more; there is usually a slight channel, as at p. all round the top of the stem. When a mushroom is perfectly ripe and the gills are brown-black in colour, they throw down a thick dusty deposit of fine brown-black or purple-black spores; it is essential to note the colour. The spores on germination make a white felted mat, more or less dense, of mycelium; this, when compacted with dry, half-decomposed dung, is the mushroom spawn of gardeners. The stem is firm, slightly pithy up the middle, but never hollow; it bears a floccose ring near its middle, as illustrated at q, q; this ring originates by the rupture of the thin general wrapper k of the infant plant.

Like all widely spread and much-cultivated plants, the edible mushroom has numerous varieties, and it differs in different places and under different modes of culture in much the same way as our kitchen-garden plants differ from the type they have been derived from, and from each other. In some instances these differences are so marked that they have led some botanists to regard as distinct species many forms usually esteemed by others as varieties only.

Fig. 1.—Pasture Mushroom (Agaricus campestris).

A small variety of the common mushroom found in pastures has been named A. pratensis; it differs from the type in having a pale reddish-brown scaly top, and the flesh on being cut or broken changes to pale rose-colour. A variety still more marked, with a darker brown cap and the flesh changing to a deeper rose, and sometimes blood-red, has been described as A. rufescens. The well-known compact variety of mushroom-growers, with its white cap and dull purplish clay-coloured gills, is A. hortensis. Two sub-varieties of this have been described under the names of A. Buchanani and A. elongatus, and other distinct forms are known to botanists. A variety also grows in woods named A. silvicola; this can only be distinguished from the pasture mushroom by its elongated bulbous stem and its externally smooth cap. There is also a fungus well known to botanists and cultivators which appears to be intermediate between the pasture variety and the wood variety, named A. vaporarius. The large rank horse mushroom, now generally referred to as A. arvensis, is probably a variety of the pasture mushroom; it grows in rings in woody places and under trees and hedges in meadows; it has a large scaly round cap, and the flesh quickly changes to buff or brown when cut or broken; the stem too is hollow. An unusually scaly form of this has been described as A. villaticus and another as A. augustus.

A species, described by Berkeley and Broome as distinct from both the pasture mushroom and horse mushroom, has been published under the name of A. elvensis. This grows under oaks, in clusters—a most unusual character for the mushroom, and is said to be excellent for the table. An allied fungus peculiar to woods, with a less fleshy cap than the true mushroom, with hollow stem, and strong odour, has been described as a close ally of the pasture mushroom under the name of A. silvaticus; its qualities for the table have not been recorded.

Many instances are on record of symptoms of poisoning, and even death, having followed the consumption of plants which have passed as true mushrooms; these cases have probably arisen from the examples consumed being in a state of decay, or from some mistake as to the species eaten. It should always be specially noted whether the fungi to be consumed are in a fresh and wholesome condition, otherwise they act as a poison in precisely the same way as does any other semi-putrid vegetable. Many instances are on record where mushroom-beds have been invaded by a growth of strange fungi and the true mushrooms have been ousted to the advantage of the new-comers. When mushrooms are gathered for sale by persons unacquainted with the different species mistakes are of frequent occurrence. A very common spurious mushroom in markets is A. velutinus, a slender, ringless, hollow-stemmed, black-gilled fungus, common in gardens and about dung and stumps; it is about the size of a mushroom, but thinner in all its parts and far more brittle; it has a black hairy fringe hanging round the edge of the cap when fresh. Another spurious mushroom, and equally common in dealers' baskets, is A. lacrymabundus; this grows in the same positions as the last, and is somewhat fleshier and more like a true mushroom; it has a hollow stem and a slight ring, the gills are black-brown mottled and generally studded with tear-like drops of moisture. In both these species the gills distinctly touch and grow on to the stem. Besides these there are numerous other black-gilled species which find a place in baskets—some species far too small to bear any resemblance to a mushroom, others large and deliquescent, generally belonging to the stump- and dung-borne genus Coprinus. The true mushroom itself is to a great extent a dung-borne species, therefore mushroom-beds are always liable to an invasion from other dung-borne forms. The spores of all fungi are constantly floating about in the air, and when the spores of dung-infesting species alight on a mushroom-bed they find a nidus already prepared that exactly suits them; and if the spawn of the new-comer becomes more profuse than that of the mushroom the stranger takes up his position at the expense of the mushroom. There is also a fungus named Xylaria vaporaria, which sometimes fixes itself on mushroom-beds and produces such an enormous quantity of string-like spawn that the entire destruction of the bed results. This spawn is sometimes so profuse that it is pulled out of the beds in enormous masses and carted away in barrows.

Sometimes cases of poisoning follow the consumption of what have really appeared to gardeners to be true bed-mushrooms, and to country folks as small horse mushrooms. The case is made more complicated by the fact that these highly poisonous forms now and then appear upon mushroom-beds to the exclusion of the mushrooms. This dangerous counterfeit is A. fastibilis, or sometimes A. crustuliniformis, a close ally if not indeed a mere variety of the first. A description of one will do for both, A. fastibilis being a little the more slender of the two. Both have fleshy caps, whitish, moist and clammy to the touch; instead of a pleasant odour, they have a disagreeable one; the stems are ringless, or nearly so; and the gills, which are palish-clay-brown, distinctly touch and grow on to the solid or pithy stem. These two fungi usually grow in woods, but sometimes in hedges and in shady places in meadows, or even, as has been said, as invaders on mushroom-beds. The pale clay-coloured gills, offensive odour, and clammy or even viscid top are decisive characters. A reference to the accompanying illustration (fig. 2), which is about one-half natural size, will give a good idea of A. fastibilis; the difference in the nature of the attachment of the gills near the stem is seen at r, the absence of a true ring at s, and of a pendent frill at t. The colour, with the exception of the gills, is not unlike that of the mushroom. In determining fungi no single character must be relied upon as conclusive, but all the characters must be taken together. Sometimes a beautiful, somewhat slender, fungus peculiar to stumps in woods is mistaken for the mushroom in A. cervinus; it has a tall, solid, white, ringless stem and somewhat thin brown cap, furnished underneath with beautiful rose-coloured gills, which are free from the stem as in the mushroom, and which never turn black. It is probably a poisonous plant, belonging, as it does, to a dangerous cohort. Many other species of Agaricus more or less resemble A. campestris, notably some of the plants found under the sub-genera Lepiota, Volvaria, Pholiota and Psalliota; but when the characters are noted they may all with a little care be easily distinguished from each other. The better plan is to discard at once all fungi which have not been gathered from open pastures; by this act alone more than nine-tenths of worthless and poisonous species will be excluded.

Fig. 2.—Poisonous Mushroom (Agaricus fastibilis).

In cases of poisoning by mushrooms immediate medical advice should be secured. The dangerous principle is a narcotic, and the symptoms are usually great nausea, drowsiness, stupor and pains in the joints. A good palliative is sweet oil; this will allay any corrosive irritation of the throat and stomach, and at the same time cause vomiting.

Paris mushrooms are cultivated in enormous quantities in dark underground cellars at a depth of from 60 to 160 ft. from the surface. The stable manure is taken into the tortuous passages of these cellars, and the spawn introduced from masses of dry dung where it occurs naturally. In France mushroom-growers do not use the compact blocks or bricks of spawn so familiar in England, but much smaller flakes or “leaves” of dry dung in which the spawn or mycelium can be seen to exist. Less manure is used in these cellars than we generally see in the mushroom-houses of England, and the surface of each bed is covered with about an inch of fine white stony soil. The beds are kept artificially moist by the application of water brought from the surface, and the different galleries bear crops in succession. As one is exhausted another is in full bearing, so that by a systematic arrangement a single proprietor will send to the surface from 300 ℔ to 3000 ℔ of mushrooms per day. The passages sometimes extend over several miles, the beds sometimes occupying over 20 m., and, as there are many proprietors of cellars, the produce of mushrooms is so large that not only is Paris fully supplied, but vast quantities are forwarded to the different large towns of Europe; the mushrooms are not allowed to reach the fully expanded condition, but are gathered in a large button state, the whole growth of the mushroom being removed and the hole left in the manure covered with fine earth. The beds remain in bearing for six or eight months, and then the spent manure is taken to the surface again for garden and field purposes. The equable temperature of these cellars and their freedom from draught is one cause of their great success; to this must be added the natural virgin spawn, for by continually using spawn taken from mushroom-producing beds the potency for reproduction is weakened. The beds produce mushrooms in about six weeks after this spawning.

The common mushroom (Agaricus campestris) is propagated by spores, the fine black dust seen to be thrown off when a mature specimen is laid on white paper or a white dish; these give rise to what is known as the “spawn” or mycelium, which consists of whitish threads permeating dried dung or similar substances, and which, when planted in a proper medium, runs through the mass, and eventually develops the fructification known as the mushroom. This spawn may be obtained from old pastures, or decayed mushroom beds, and is purchased from nurserymen in the form of bricks charged with the mycelium, and technically known as mushroom spawn. When once obtained, it may be indefinitely preserved. It may be produced by placing quantities of horse-dung saturated with the urine of horses, especially of stud horses, with alternate layers of rich earth, and covering the whole with straw, to exclude rain and air; the spawn commonly appears in the heap in about two months afterwards. The droppings of stall-fed horses, or of such as have been kept on dry food, should be made use of.

The old method of growing mushrooms in ridges out of doors, or on prepared beds either level or sloping from a back wall in sheds or cellars, may generally be adopted with success. The beds are formed of horse-droppings which have been slightly fermented and frequently turned, and may be made 2 or 3 ft. broad and of any length. A layer of dung about 8 or 10 in. thick is first deposited, and covered with a light dryish earth to the depth of 2 in.; and two similar layers with similar coverings are added, the whole being made narrower as it advances in height. When the bed is finished, it is covered with straw to protect it from rain, and also from parching influences. In about ten days, when the mass is milkwarm, the bed will be ready for spawning, which consists of inserting small pieces of spawn bricks into the sloping sides of the bed, about 6 in. asunder. A layer of fine earth is then placed over the whole, and well beaten down, and the surface is covered with a thick coat of straw. When the weather is temperate, mushrooms will appear in about a month after the bed has been made, but at other times a much longer period may elapse. The principal things to be attended to are to preserve a moderate state of moisture and a proper mild degree of warmth; and the treatment must vary according to the season.

These ordinary ridge beds furnish a good supply towards the end of summer, and in autumn. To command a regular supply, however, at all seasons, the use of a mushroom-house will be found very convenient. The material employed in all cases is the droppings of horses, which should be collected fresh, and spread out in thin layers in a dry place, a portion of the short litter being retained well moistened by horse-urine. It should then be thrown together in ridges and frequently turned, so as to be kept in an incipient state of fermentation, a little dryish friable loam being mixed with it to retain the ammonia given off by the dung. With this or a mixture of horse-dung, loam, old mushroom-bed dung, and half-decayed leaves, the beds are built up in successive layers of about 3 in. thick, each layer being beaten firm, until the bed is 9 or 10 in. thick. If the heat exceeds 80°, holes should be made to moderate the fermentation. The beds are to be spawned when the heat moderates, and the surface is then covered with a sprinkling of warmed loam, which after a few days is made up to a thickness of 2 in., and well beaten down. The beds made partly of old mushroom-bed dung often contain sufficient spawn to yield a crop, without the introduction of brick or cake spawn, but it is advisable to spawn them in the regular way. The spawn should be introduced an inch or two below the surface when the heat has declined to about 75°, indeed the bed ought never to exceed 80°. The surface is to be afterwards covered with, hay or litter. The atmospheric temperature should range from 60° to 65° till the mushrooms appear, when it may drop a few degrees, but not lower than 55°. If the beds require watering, water of about 80° should be used, and it is preferable to moisten the covering of litter rather than the surface of the beds themselves. It is also beneficial, especially in the case of partially exhausted beds, to water, with a dilute solution of nitre. For a winter supply the beds should be made towards the end of August, and the end of October. Slugs and woodlice are the worst enemies of mushroom crops.

The Fairy-ring Champignon.—This fungus, Marasmius Oreades, is more universally used in France and Italy than in England, although it is well known and frequently used both in a fresh and in a dry state in England. It is totally different in appearance from the pasture mushroom, and, like it, its characters are so distinct that there is hardly a possibility of making a mistake when its peculiarities are once comprehended. It has more than one advantage over the meadow mushroom in its extreme commonness, its profuse growth, the length of the season in which it may be gathered, the total absence of varietal forms, its adaptability for being dried and preserved for years, and its persistent delicious taste. It is by many esteemed as the best of all the edible fungi found in Great Britain. Like the mushroom, it grows in short open pastures and amongst the short grass of open roadsides; sometimes it appears on lawns, but it never occurs in woods or in damp shady places. Its natural habit is to grow in rings, and the grassy fairy-rings so frequent amongst the short grass of downs and pastures in the spring are generally caused by the nitrogenous manure applied to the soil in the previous autumn by the decay of a circle of these fungi. Many other fungi in addition to the fairy-ring champignon grow in circles, so that this habit must merely be taken with its other characters in cases of doubt.

Fig. 3.—The Fairy-ring Champignon (Marasmius oreades).

A glance at the illustration (fig. 3) will show how entirely the fairy-ring champignon differs from the mushroom. In the first place, it is about one-half the size of a mushroom, and whitish-buff in every part, the gills always retaining this colour and never becoming salmon-coloured, brown or black. The stem is solid and corky, much more solid than the flesh of the cap, and perfectly smooth, never being furnished with the slightest trace of a ring. The buff-gills are far apart (v), and in this they greatly differ from the somewhat crowded gills of the mushroom; the junction of the gills with the stem (w) also differs in character from the similar junction in the mushroom. The mushroom is a semi-deliquescent fungus which rapidly falls into putridity in decay, whilst the champignon dries up into a leathery substance in the sun, but speedily revives and takes its original form again after the first shower. To this character the fungus owes its generic name (Marasmius) as well as one of its most valuable qualities for the table, for examples may be gathered from June to November, and if carefully dried may be hung on strings for culinary purposes and preserved without deterioration for several years; indeed, many persons assert that the rich flavour of these fungi increases with years. Champignons are highly esteemed (and especially is this the case abroad) for adding a most delicious flavour to stews, soups and gravies.

A fungus which may carelessly be mistaken for the mushroom is M. peronatus, but this grows in woods amongst dead leaves, and has a hairy base to the stem and a somewhat acrid taste. Another is M. urens; this also generally grows in woods, but the gills are not nearly so deep, they soon become brownish, the stem is downy, and the taste is acrid. An Agaricus named A. dryophilus has sometimes been gathered in mistake for the champignon, but this too grows in woods where the champignon never grows; it has a hollow instead of a solid stem, gills crowded together instead of far apart, and flesh very tender and brittle instead of tough. A small esculent ally of the champignon, named M. scovodonius, is sometimes found in pastures in Great Britain; this is largely consumed on the Continent, where it is esteemed for its powerful flavour of garlic. In England, where garlic is not used to a large extent, this fungus is not sought for. Another small and common species, M. porreus, is pervaded with a garlic flavour to an equal extent with the last. A third species, M. alliaceus, is also strongly impregnated with the scent and taste of onions or garlic. Two species, M. impudicus and M. foetidus, are in all stages of growth highly fœtid. The curious little edible Agaricus esculentus, although placed under the sub-genus Collybia, is allied by its structure to Marasmius. It is a small bitter species common in upland pastures and fir plantations early in the season. Although not gathered for the table in England, it is greatly prized in some parts of the Continent.

  1. The earlier 15th-century form of the word was musseroun, muscheron, &c., and was adapted from the French mousseron, which is generally connected with mousse, moss.