Abstract
Liberation of conidia of Pyricularia oryzae Cav. from a newly formed lesion on a leaf or a detached node of rice plant placed in dark box (30×35×60 cm) and sedimentation of the liberated conidia were observed. The box has a slit (4×30 mm) for Tyndall illumination and has a window for observation. The sedimentation path of conidium was photographed by using a motor driving 35 mm-camera or a 8 mm-movie camera under the illumination. Liberation of conidia occurred after maturation of conidia on the lesion under 100% relative humidity and the conidium was observed to sediment singly in the box. Terminal velocity of sedimenting conidium was varying from 4.0 to 8.7 mm/sec in still air. Average value was 6.7 mm/sec by the method using 35 mm-camera and 7.0 mm/sec by the movie method. The value is of the order expected from McCubbin's empirical formula, but less than the one expected from Stoke's formula.
