Obligate Parasitism

Abstract

THE phenomenon of obligate parasitism is well known among the fungi, particularly the rusts and the powdery mildews. That the rust derives its nutrients from the host has been accepted a priori, since no other source of food for the fungus was possible. Yet the fact that the nutrients from the soil were furnished to the fungus through the plant system has not been demonstrated. Radio-phosphorus, P³², which is not changed by the plant, furnished a simple means of showing that the nutrient actually comes through the host plant.