This section is from the book "Our Edible Toadstools and Mushrooms and How to Distinguish Them", by W. Hamilton Gibson. Also available from Amazon: Our Edible Toadstools And Mushrooms And How To Distinguish Them.
Among the wild species of mushrooms which the novice might possibly mistake for the common "mushroom" of the markets - which is popularly supposed to be the only edible variety, as distinguished from "toadstools" - is the Russula group. They are extremely frequent in our woods from spring to late autumn, and have many features in common. Their caps vary in color from a gray-green, suggesting cheese-mould, to olive-red, scarlet-red, and purplish. The gills are generally of the same length, or practically so, occasionally double-branched, beginning at the stem and usually extending to the rim of the cap, at which portion they are covered by the mere skin of the pileus, a slightly fluted appearance being observable from above, which indicates the location of the radiating laminae below (Plate 12, fig. 6).
The stem may be white or cream-colored, or perhaps stained or mottled with the color of the cap.
There are at least four of these edible Russulae that we are certain of meeting in our walks in the woods: The green Russula (Russula viresceus), with its mottled cap of mouldy or sage green; the various-gilled Russula (Russula heterophylla), varying in the lengths of its gill plates; the purple Russula (Russula lepida), whose cap varies from bright red to dull purple; and the red Russula (Russula alutacea), which presents a variety of shades of red, from bright to dull. Having once identified the Russula as a group, or the common characteristics of the genus, we may take our pick from all of these delicious species for the table; but we must avoid one other member of the genus, also quite common, and which frequently masquerades in the guise of some of the bright red varieties above mentioned. This is the Russula emetica, whose obnoxious qualities are indicated by its classical surname, and which will be separately considered.