One is often asked the question: "How do you tell the mushrooms from the toadstools?" This implies that mushrooms are edible and that toadstools are poisonous, and this belief is very widespread in the public mind. The fact is that many of the toadstools are edible, the common belief that all of them are poisonous being due to unfamiliarity with the plants or their characteristics. Some apply the term mushroom to a single species, the one in cultivation, and which grows also in fields (_Agaricus campestris_), and call all others toadstools. It is becoming customary with some students to apply the term mushroom to the entire group of higher fungi to which the mushroom belongs (_Basidiomycetes_), and toadstool is regarded as a synonymous term, since there is, strictly speaking, no distinction between a mushroom and a toadstool. There are, then, edible and poisonous mushrooms, or edible and poisonous toadstools, as one chooses to employ the word. A more pertinent question to ask is how to distinguish the edible from the poisonous mushrooms. There is no single test or criterion, like the "silver spoon" test, or the criterion of a scaly cap, or the presence of a "poison cup" or "death cup," which will serve in all cases to distinguish the edible from the poisonous. Two plants may possess identical characters in this respect, i. e., each may have the "death cup," and one is edible while the other is poisonous, as in _Amanita cæsarea_, edible, and _A. phalloides_, poisonous. There are additional characters, however, in these two plants which show that the two differ, and we recognize them as two different species. To know several different kinds of edible mushrooms, which occur in greater or less quantity through the different seasons, would enable those interested in these plants to provide a palatable food at the expense only of the time required to collect them. To know several of the poisonous ones also is important, in order certainly to avoid them. The purpose of this book is to present the important characters which it is necessary to observe, in an interesting and intelligible way, to present life-size photographic reproductions accompanied with plain and accurate descriptions. By careful observation of the plant, and comparison with the illustrations and text, one will be able to add many species to the list of edible ones, where now perhaps is collected "only the one which is pink underneath." The chapters 17 to 21 should also be carefully read.