Abstract
1. Using living midrib cells of plants, the writer made microscopical observations on the protoplasmic changes induced by the infection of Phytophthora infestans.
2. In the highly resistant variety, acceleration of the appearance of protoplasmic strands, the migration of the nucleus towards the infected part, and the rhythmic movement of the nucleus around the infected part were observed in the early stage of penetration of P. infestans. These activated visible movements in the infected cell may possibly be due to the enhanced motive force of the protoplasmic streaming in that cell. This acceleration of protoplasmic movement in the infected cell was more remarkable in the resistant variety than in the susceptible one.
3. The number of protoplasmic strands in which the particles flow towards infected part is remarkably greater than that of the strands in which the particles flow in the opposite direction. So it seems that the motive force of the protoplasmic streaming is stronger in the direction towards the site of infection than in the contrary direction. The migration of the nucleus towards the site of infection may be resulted from this polarity of the motive force in the infected cell.
4. It is presumed that the enhanced motive force in the infected cell of the resistant variety may be concerned with the increased energy metabolism in the infected tissues.
