became necessary to consider its alternate hosts and biologic specialization. Altho these phases have received extensive investigation in Europe by de Bary, Eriksson, Klebahn, and others, yet they have scarcely been considered in America. On purely theoretical grounds, it would be unusual to expect the same conditions to exist in America, where there are different species of Rhamnus and grasses, as well as different climatic and environmental conditions. In fact, enough work has already been done by Carleton, Arthur, and Melhus and Durrell, on the relation of crown rust to Rhamnus and on biologic specialization, to indicate clearly that the results in America should be different.