Some histological observations on the diseased tissues of adult rice plants affected by Piricularia oryzae have been done. The diseased portion of an affected leaf may be divided into three zones. They are venenate, necrotic, and disintegrated ones. The venenate zone occupies the border of a diseased portion, often showing a long, light yellowish stripe, and blends gradually into healthy tissue. The necrotic zone forms a brown coloured, narrow streak, developing along the inner side of the venenate zone, or along the vascular bundle within affected part. The disintegrated zone is grayish brown and is in somewhat dried state occupying the most part of a diseased portion. A toxic substance, excreted by the fungus which has entered the host plant, seems to infiltrate into the surrounding tissues of the invaded portion, resulting in the formation of the venenate zone. The pathological changes of tissues of this zone are observed as follows: the discoloration and the decrease of size of chloroplast, the degeneration of cell-membrane, and the vacuolar or granular disintegration of protoplasm. When the fungous hyphae spread vigorously within the tissues of the venenate zone, the cell-inclusions as well as the cell-walls will be severely collapsed. The disintegrated zone is formed in this manner. If the poisoning action of the fungus is not so strong or the venenation of the tissue is not so severe, owing to the position of the tissue, e. g., the portion arround the vessel, some part of the cell-inclusions together with the cell-walls will remain without being wholly disintegrated, and will increase their staining properties. Thus the necrotic zone will make its appearance. The results of some observations on the culm blasts have been given. The majorities of them are the blasts of the nodes of racheae, of the bases of ears, and of the nodes of flag leaves. Many of the pathological changes of these parts are similar to that of leaf blast, with the exception of the presence of reserve starch grains, though of comparatively small amount, distributed irregulary within the tissues severely affected. The decrease of starch in the affected tissues may be attributed to the transformation of reserve starch into sugar, carried out within the tissues, affected but still living. Because, the transformation of starch will begin when sugar in the cell-sap decreases in its concentration, being digested by the pathogene. It is also advocated that the irregular distribution of starch remains in the severely affected tissues depends upon the feeble diastatic action of the pathogene, Piricularia oryzae.
The rice plants of several varieties had been subjected to various treatments to make wounds on the leaves. These plants were then atomized with suspension of the conidia of Piricularia oryzae, developed on steamed straw. The counts of the number of diseaed patches on the leaves were made. The results may be summarized as follows; The leaves injured by having been filed their surfaces, or bent at the base of the leaf blades, or cut of the midribs, produced invariably more numerous patches than the untreated leaves. Under condifions of poor nutrition, the injured leaves showed relatively a large number of patches, although the intact leaves produced none or very few. The plants which were shaken violently before inoculation, were affected heavily than the untreated plants. From the results obtained, it may be considered that the cuticular layer of the leaf plays possibly an important rôle in presenting resistance of rice plants to the blast disease.
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.