“ The corn-mildew, the hop-mildew and the vine-mildew are, for example, parasitic upon living plants, and the mildews of damp linen and of paper are saprophytes (Gr. σαπρός, rotten) , that is, they subsist on matter which is already dead. As regards mildews in general, the conditions of life and growth are mainly suitable nutrition and dampness accompanied by a high temperature. The life history of the same species of mildew frequently covers two or more generations, and these are often passed on hosts of different kinds. ”