No botanic distinction exists between toadstools and mushrooms; mushrooms may be regarded as edible toadstools. They are all, botanically speaking, edible or poisonous fungi. A description follows of the five kinds of fungi most commonly eaten, and the poisonous species which may be mistaken for them.
=EDIBLE MUSHROOMS.=--=1. The Common Mushroom= (_Agaricus Campestris_).--The fungi called agarici are those which have gills, that is, little plates which look like knife blades on the under surface of the top of the mushroom, radiating outward from the stem like the spokes of a wheel. This is the species most frequently grown artificially, and sold in the markets. The top or cap of this mushroom is white, or of varying shades of brown, and measures from one and a half to three or even four inches in diameter. It is found in the latter part of August, in September, and in October, growing in clusters on pastures, fields, and lawns.
The gills are pink or salmon colored in the newly expanded specimen; but as it grows older, or after it is picked, the gills turn dark purple, chestnut brown, or black. This is the important point to remember, since the poisonous species mistaken for it all have white gills. The gills end with abrupt upward curves at the center of the cap without being attached to the stem. In the young mushroom, when the cap is folded down about the stem, the gills are not noticeable, as they are covered by a veil or filmy membrane, a part of which remains attached to the stem (when the top expands), as a ring or collar about the stem a little more than halfway up from the ground. The stem is solid and not hollow, and there is no bulbous enlargement at the base of the stem, surrounded by scales or a collar, as occurs in the _fly amanita_ and other poisonous species. Neither the _campestris_ nor any other mushroom should be eaten when over a day old, since decomposition quickly sets in.
=2. Horse Mushroom= (_Agaricus Arvensis_).--This species may be considered with the foregoing, but it differs in being considerably larger (measuring four to ten inches across) and in having a more shiny cap, of a white or brown hue. The ring about the stem is noticeably wider and thicker, and is composed of two distinct layers. The gills are white at first, turning dark brown comparatively late, and the stem is a little hollow as it matures. In some localities it is more common than the _campestris_ in fields and pastures, while in other places it is found only in rich gardens, about hot beds, or in cold frames. It is not distinguished from the _campestris_ by market people, but is often sold with the latter.