1. The present paper deals with the results of experiments on the effect of sunlight upon the infection of the rice plant by Ophiobolus Miyabeanus, to the germination of its conidia and also to the disease-development. 2. Rice seedlings are more abundantly infected in the absence of light than in the presence of light. 3. The percentage of conidial germination of the causal fungus and also the length of its germ-tubes are greater in the absence of light than in the presence of light. 4. Using four glass boxes kept under the same conditions except light intensity, the writer has carried out an experiment on the effect, upon the development of the disease, of shading after inoculation. The number of diseased lesions per unit length of the leaf was maximum on the seedlings kept in the box covered with two sheets of cotton cloth and minimum on those in the box covered with black paper. The seedlings, kept in the boxes uncovered or covered with a single sheet of cotton cloth, showed the medium number of lesions. 5. Using the same boxes, the writer carried out an experiment on the effect, upon the disease development of rice seedlings, of shading before inoculation. The number of diseased lesions per unit length of the leaf was maximum on the seedlings kept in the box covered with a single sheet and minimum on those in the box covered with two sheets of cotton cloth. The seedlings, kept in the boxes covered with black paper or uncovered, showed the medium number of lesions.
This paper deals with the entrance and migration of Bacterium solanacearum SMITH in tobacco plants. The inoculation on stems, roots, and leaves made with the organism cultured on potato agar or potato decoction showed that infection took place only through the wound and never occurred in the stomata or water pores except in the case of stigma where infection occurred without wound. The unwound roots, however, have been infected by the bacteria cultured in milk which makes them more virulent than potato agar or potato decoction. In young stems and leaves the bacteria at first occupied the xylem tubes, entering through the wound and then grew outwards from these tubes to the surrounding tissues, which were found to be badly disintegrated. The bacterial cavities were often observed within the pith and cortex of the stems. The distance of the downward movement of the bacteria in the xylem tubes is greater than that of upward movement. After 24 hours from inoculation on the young stems kept at 25°C, the bacteria moved upwards and downwards at the rates of 0.2586mm and 0.2692mm an hour respectively. The rate of migration was the most rapid at 32°C and slower at 37°C than at 20°C, the maximum and minimum rates for migration being considered at 15°C and 40°C.