Abstract
1. The present paper deals with the development and structure of the haustorium and its vesicle in some powdery mildews.
2. Upon the stripped epidermis of onion bulbs and leaves of plant, treated with alcohol and washed in water, germination of the conidiospores takes place better than upon the living leaves, even of the proper host plant.
3. Chemical stimulus from the host cell does not seem to be concerned with the formation of the infection hypha.
4. Two types of the haustoria are distinguished in epiphytic powdery mildews: the one being represented by Erysiphe graminis and the other by E. cichoracearum. In both types processes are formed on the both ends of the ellipsoidal body of the haustorium, but in the former type they extend straightly like fingers and in the latter assume a covnolute form covering the body.
5. The young haustorium is in direct contact with the host plasm and the mature one is always encased in a vesicle which is filled with a transparent liquid. Generally the vesicle makes its appearance near the neck of the haustorium, extending over the whole surface of the body, and increases its diameter as the haustorium develops, showing a turgid state.
6. In solutions of neutral salts, even ones poisonous to the host cell, the vesicle is much swollen. Strong bases and inorganic acids have a conspicuous effect upon the vesicle.
7. The vesicle is stainable with various stains, some of which are proved to stain the vesicular membrane itself.
8. The derivation of the vesicle is not detemined, and only three possible cases are considered.
9. As the haustorium becomes older, the processes on its surface become indistinct and the vesicle loses turgidity and at last the outline of the haustorium becomes indistisnguishable.
10. The haustorium vesicle of the powdery mildew on Sedum is surrounded by a brown refractive substance, which appears to be deposited from the host plasm.
