This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
In the selection of mushrooms to eat, great caution should be employed by those who are not reasonably familiar with the means of determination of the species, or those who have not an intimate acquaintance with certain forms. Rarely should the beginner be encouraged to eat them upon his own determination. It is best at first to consult some one who knows, or to send first specimens away for determination, though in many cases a careful comparison of the plant with the figures and descriptions given in this book will enable a novice to recognize it. In taking up a species for the first time it would be well to experiment cautiously.
There is no certain test, like the "silver spoon test," which will enable one to tell the poisonous mushroom from the edible ones. Nor is the presence of the so-called "death cup" a sure sign that the fungus is poisonous, for the Amanita caesarea has this cup. For the beginner, however, there are certain general rules, which, if carefully followed, will enable him to avoid the poisonous ones, while at the same time necessarily excluding many edible ones. 1st. - Reject all fungi which have begun to decay, or which are infested with larvae. 2d. - Reject all fungi when in the button stage, since the characters are not yet shown which enable one to distinguish the genera and species. Buttons in pasture lands which are at the surface of the ground and not deep-seated in the soil, would very likely not belong to any of the very poisonous kinds. 3d. - Reject all fungi which have a cup or sac-like envelope at the base of the stem, or which have a scaly or closely fitting layer at the base of the stem, and rather loose warts on the pileus, especially if the gills are white. Amanita caesarea has a sac-like envelope at the base of the stem, and yellow gills as well as a yellow cap, and is edible. Amanita rubescens has remnants of a scaly envelope on the base of the stem and loose warts on the cap, and the flesh where wounded becomes reddish. It is edible. (See plate 19.) 4th. - Reject all fungi with a milky juice unless the juice is reddish. Several species with copious white milk, sweet or mild to the taste, are edible (see Lactarius volemus and corrugis). Sth. - Reject very brittle fungi with gills nearly all of equal length, where the flesh of the cap is thin, especially those with bright caps. 6th. - Reject all Boleti in which the flesh changes color where bruised or cut, or those in which the tubes have reddish mouths, also those the taste of which is bitter. Strobilomyces strobilaceus changes color when cut, and is edible. 7th - Reject fungi which have a cobwebby veil or ring when young, and those with slimy caps and clay-colored spores. In addition, proceed cautiously in all cases, and make it a point to become very familiar with a few species first, and gradually extend the range of species, rather than attempt the first season to eat a large number of different kinds.
All puff-balls are edible so long as they are white inside, though some are better than others. All coral-like or club fungi are edible. To Clean and Prepare the Specimens. - The mushrooms having been collected, all tough stems, the parts to which earth clings, should be removed. After the specimens are selected, if there is danger that some of them may be infested with larvae, it is well to cut off the stem close to the cap, for if the insects are in the stem and have not yet reached the cap they may thus be cast away. Some recommend that the tubes of all Boleti be removed, since they are apt to make a slimy mass in cooking.
Where the plants are small they may be cooked entire. Large ones should be quartered, or cut, or sliced, according to the size and form of the plant, or method of cooking.