MUSHROOM. The edible fungus of this name is known botanically as Agaricus campestris or Psalliota campestris. It grows in short grass in the temperate re gions of all parts of the world. Many edible fungi depend upon minute and often ob scure botanical characters for their de termination, and may readily be con founded with worthless or poisonous spe cies ; but that is not the case with the common mushroom, for, al though 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 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 product of short, up land, 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 of inferior flavour. The mushroom usually grown in gardens or hot-beds, in cellars, sheds, etc., is a distinct species known as Agaricus horten sis. 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 char
acters are taken together no other mushroom-like fungus—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, free from the stem. The cap 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 thick flesh beneath. The cap has a narrow de pendent margin or frill ; this originates in the rupture of a deli cate continuous wrapper, which in the infancy of the mushroom entirely wraps the young plant. The gills underneath the cap are at first white, then rose-coloured, finally brown-black. A point of great importance is to be noted in the attachment of the gills near the stem; the gills in the true mushroom are, however, 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 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 stem is firm, slightly pithy up the middle, but never hollow; it bears a floccose ring near its middle; this originates by the rupture of the thin general wrapper 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.