The present booklet is the fourth of a series of popular guides to the plants of Minnesota, designed for plant-lovers and for classes in botany in high school and college. An equally important object Of the guide to mushrooms is to make available with safety the enormous annual crop of mushrooms, which is now almost entirely wasted through fear or neglect. It is perhaps idle to estimate the size or value of this crop, but if that part which is readily accessible is alone considered, the number of pounds will reach into the hundred thousands. Figured on the market price of the cultivated mushroom, the total value of the mushroom crop of the State can hardly be less than a million dollars. Just what would be the effect Of utilizing this food supply is a matter of conjecture, but there can be little doubt that it would prove fortunate from the standpoint of dietetics as well as Of economics.