Hence the questions with the beginner is, how he may tell a poisonous fungus from an edible one. There is but one answer to this question, and that is that he must thoroughly learn both genera and species, studying each till he knows its special features as he does those of his most familiar friends.
Certain species have been tested by a number of people and found to be perfectly safe and savory; on the other hand, there are species under various genera which, if not actually poisonous, are at least deleterious.
It is the province of all books on fungi to assist the student in separating the plants into genera and species; in this work special attention has been given to distinguishing between the edible and the poisonous species. There are a few species such as Gyromitra esculenta, Lepiota Morgani, Clitocybe illudens, etc., which when eaten by certain persons will cause sickness soon after eating, while others will escape any disagreeable effects. Chemically speaking, they are not poisonous, but simply refuse to be assimilated in some stomachs. It is best to avoid all such.
=HOW MUSHROOMS GROW.= There is a strong notion that mushrooms grow very quickly, springing up in a single night. This is erroneous. It is true that after they have reached the button stage they develop very quickly; or in the case of those that spring from a mature egg, develop so rapidly that you can plainly see the motion of the upward growth, but the development of the button from the mycelium or spawn takes time--weeks, months, and even years. It would be very difficult to tell the age of many of our tree fungi.
=HOW TO LEARN MUSHROOMS.= If the beginner will avoid all Amanitas and perhaps some of the Boleti he need not be much worried in regard to the safety of other species.
There are three ways by which he can become familiar with the edible kinds. The first is the physiological test suggested by Mr. Gibson in his book. It consists in chewing a small morsel and then spitting it out without swallowing the juice; if no important symptoms arise within twenty-four hours, another bit may be chewed, this time swallowing a small portion of the juice. Should no irritation be experienced after another period of waiting, a still larger piece may be tried. I always sample a new plant carefully, and thus am often able to establish the fact of its edibility before being able to locate it in its proper species. This fall I found for the first time Tricholoma columbetta; it was some time after I had proven it an edible mushroom before I had settled upon its name. A better way, perhaps, is to cook them and feed them to your cat and watch the result.