The genus Lactarius is one of the two major genera in the Russulaceae. This large family of mushrooms is mostly woodland inhabiting and form mycorrhiza with various species of woody vascular plants. Lactarius and Russula together comprise the most conspicuous element in the summer mushroom flora in North America. But in spite of this, knowledge of both genera has been slow to accumulate until now. North American Species of Lactarius, by L. R. Hesler and Alexander H. Smith, is the most comprehensive investigation of Lactarius for the United States and Canada yet published.