Mushroom, or Agaricus, L. a genus of plants, comprising numerous species, of which more than 300 are natives of Britain ; among these, the following deserve to be specified :

1. The semi-g/obatus, or Semi-globular Mushroom, the gills or under part of which are fixed, and when quite young, of a whitish colour: the edges soon become entirely grey or mottled ; and, when old, acquire a chocolate tinge. The stem is hollow, growing two or three inches high, and about the size of a crow's-quill. This species is found in great abundance on, grass-plats, and on pastures, chiefly between the months of July and October ; when it ought to be carefully avoided, being one of the poisonous fungi, the inadvertent eating of which has frequently proved fatal.

2. The muscarius (Musky), or rather Fly-killing, Reddish Mushroom, has a large head, which is nearly flat, being generally either white, reddish, or of a crimson hue, and covered with raised, compact, angular warts, that are sometimes thin, ragged, and flat. Its stem is solid, but the pith, or internal substance, shrivels as it becomes old, leaving irregular cavities : it grows in pastures from three to five inches in height, and is from three quarters to an inch and a half, in diameter. Among fir-trees, its head is sometimes twelve inches broad, and the stem from four to six inches high. - This species is also poisonous ; and, if mixed with milk is said to destroy flies : the expressed juice from this plant, when rubbed on walls and bedsteads, has been employed to expel bugs.—Gesenius, a medical author of great reputation, observes, that the celebrated nostrum sold at Frankfort, in Germany, under the name of Ragolo's Anti -epileptic powders, is supposed to consist of the Reddish Mushroom-mixed with distilled oil, and pulverized valerian : this remedy is considered, on the Continent) as the only safe and certain specific for the cure of that dreadful malady.

3. The clypeatus, or Long-stalked Mushroom, which has a hollow, white, viscid, tender stem, that grows to the height of four inches; and is, in general, not thicker than a crow's - quill. It is found in the month of September, in wood-lands and pastures; is highly deleterious ; and, if impro-vidently eaten, causes great swelling, sickness, looseness, and other fatal symptoms.

These are the principal poisonous species growing in this country ; but there are doubtless many others, equally pernicious, though not generally known. — On the other hand, the harmless and esculent mushrooms, are chiefly the following :

4. The campestris, Champignon, or Common Mushroom, the stem of which is solid and white, usually 3-4ths of an inch high, and of the thickness of a swallow's quill. Its gills, when first expanded, are of a bright-red colour, which gradually acquires a darker shade, till they become of a deep-brown cast. This plant at first represents a small globular figure, not unlike a hazle-nut; in which state it is free from worms, and eatable ; as the skin, in which it is enveloped, may then be easily separated from its white, juicy flesh : by this circumstance, it will be readily distinguished from a similar plant, the agaricus vermis, which is said to be poisonous.- The common mushroom is found in woods, old pastures, and at the side of roads, where it attains to perfe£tion in the month of September.

5. The orcades, v. pratensis, or Meadow Mushroom (by some also called champignon) is very frequent on heaths, and dry pastures, being generally found in circular clusters. The cap is of a pale brown, nearly flat, and from one to three inches in diameter. Its stem is very tough, solid, and white; grows generally to the height of an inch and a half, and as thick as a crow's quill.- This species is also eatable in September : it possesses but little smell, while raw, and is somewhat dry; yet, when broiled or stewed, it imparts a pleasant flavour.

6. The cantharellus (Merulius cantharellus of WitheRing), or Chantarelle Mushroom, is wholly of a yellow cast, similar to that of the yolk of an egg. Its stem is solid, tapering downwards, being from one to two inches high, and from l-4th to 3-4ths of an inch in diameter. It is found in woods and dry pastures, from July to September. This plant, when boiled with salt and pepper, possesses the flavour of a roasted cockle: it is esteemed, together with the preceding species, as a great delicacy.

7. The deliciosus, or Orange-coloured Mushroom, grows from, one to two inches high: its stem is from l-4th to 3-8ths of an inch in diameter, and is crowned with a flat cap, from one one-half to three inches broad, and of a rich reddish-brown colour; but its flesh is of a pale orange cast.- In its sensible properties, this species is similar to the preceding. It is in season in the month of September, and is found in dry and elevated woods.- The Italians, especially at Genoa, preserve it in olive-oil, and esteem it as great a delicacy as the celebrated boletus of the Romans. There are, however, two other varieties greatly resembling the orange-coloured eatable mushroom, but which are in a high degree poisonous ; especially the tor-minosus (piperatus of Withering), which grows on the roots of birch-trees, for instance, atHaugh-wood near Woolhope, Herefordshire ; and the necator, which is of a dirty yellowish cast, appears to be composed of woolly fibres filled with a glutinous dew ; and thrives in the same place, as well as in the park at Edgbaston, under large Spanish chesnut-trees.

8. The cinnamomeus, or Brown Mushroom, has a convex, but flatted, clothy cap; often with a central rise, in colour resembling that of a chesuut, or newly tanned leather. Its long stem is yellowish and naked, and the gills tawny red. This plant is readily distinguished by its cinnamon colour: in the months of September and October, it abounds in woods, especially in the plantations at Tettenhall, Staffordshire, and at Peudarvis, in Cornwall: it emits an agreeable odour, and, when boiled, possesses a fine flavour.

9. The violaceus, or Violet-co-V>ured Mushroom, has numerous purple gills, eight in a set: the cap being of a purple or brown cast, convex, and the edge turned down ; the stem is also purple and cylindrical, from 1/4 to one inch in diameter, and growing from one to four inches in height, - This species remarkably varies, both in its size and tints. When full grown, the cap changes its lilac colour to a russet hue; but the gills continue nearly in the same state; hence, according to Major Velley, the latter afford a more accurate criterion, with respect to colour, than any other part of mushrooms in general.- The violet-coloured mushroom is in perfection from October to December, and is frequently found at Edgbaston and Barr Plantations, in the woods near Bath, and at Powick, near Worcester. - When thoroughly boiled and seasoned, it is asserted to be as palatable as an oyster.

We have now enumerated the principal species of mushrooms that are poisonous, as well as those which may be safely eaten; but, as their harmless, or noxious properties, in a great measure depend on the nature and situation of the soil producing them, it will always be necessary to attend to this circumstance, before they are gathered. There is no doubt but that the gills inhale the stagnant or superfluous vapours from the ground ; hence, they speedily putrefy, and become the prey of worms, flies, and other insects.

In horticulture, the esculent mushrooms only are raised artificially ; for this purpose, when no young plants can be procured from the fields or gardens, their roots, spawn, or embryons, may be generated from horse-dung, laid unbroken in small heaps, under cover. In a few weeks, during the summer months, fibrous roots will appear, resembling white threads, which, on separating the heaps, emit the smell of mushrooms.

The dung is directed to be carefully piled up, as entire as possible, about three inches thick, on a hot-bed of a moderate heat; and formed of alternate strata of horse-dung, and tanner's-waste ; the uppermost layer being composed wholly of tan, to the thickness of two inches. The bed is next to be covered with a little manure, and to be raised about three inches, with good soil, when it is finally overspread with a thick stratum, or coat of straw.

The most proper place for the formation of mushroom-beds, is in the shed usually erected behind hot-houses ; because, as these plants vegetate without light, warmth only is requisite, provided they be occaOccasionally watered.- The French practise a method of rearing these plants, which is both simple and expeditious : they pour the water, that has been employed for washing eatable mushrooms, on the usual hot-beds, and thus a con- stant succession of growth is obtained, especially if the stalks be left in the ground, when their heads or caps are gathered for the table.—In China, the putrefied wood of elms and willows is form-into a bed, and covered with the leaves of these trees; the whole is then frequently watered with a weak solution of nitre. This composition produces continual crops of the most delicious champignons, which are collected in the manner before stated.

Mushrooms form an isthmus between the animal and vegetable kingdoms ; and it is not yet ascertained, whether they can be propagated by seed. When in a state of putrefaction, they emit a cadaverous smell; and it appears from the experiments of Von Humboldt, that they are equally good conductors of Galvanism, or of the Galvanic Fluid, as real animal matters. He farther observes, that their participation of animal nature is evinced by chemical analysis ; because mushrooms contain a remarkable portion of azote and phosphorus; and morels may be converted into fat, by means of the sulphuric acid, or oil of vitriol, diluted with water.

Considered as an article of food, mushrooms are by no means wholesome or nourishing : being tough, and greatly resembling soft leather, they are almost indigestible, and ought not to be eaten by persons of weak or inactive stomachs. Besides, many species of this numerous genus of vegetables are extremely deleterious, and cannot be accurately distinguished from such as are harmless and esculent: it would not, therefore, be attended with any loss, excepting to the epicure, if mushrooms were totally banished from our tables. But, if they must be dressed, it will be advisable to employ a large portion of vinegar, or other vegetable 3cids, to counteract their acrimonious and narcotic nature. - In order to ascertain, with greater certainty, whether all the plants of a collectiion which is destined to undergo the culinary process, be of an inoffensive nature, it will be proper to put a peeled onion in the vessel in which they are to be cooked ; and, if this root acquire a blueish or dark hue, we may conclude that there doubtless are poisonous mushrooms among them. Should, however, any noxious species have been inadvertently eaten, it will be requisite to take a dose of ipecacuanha, or of the an-timonial emetics, in order to eject the poison as speedily as possible; or, if the accident be discovered only after some hours have elapsed, copious draughts of vinegar and water, or oil and vinegar, will then form the most efficacious antidotes.