抄録
l. Using the main axis of caster-bean plant, Ricinus communis, the histological change caused by applying α-naphthalene acetic acid was compared with that shown by the same organ kept horizontally as a result of georeaction. The purpose was to obtain an experimental evidence concerning the cause of the latter case. 2. A conspicuous growth in thickness was seen at the acid-treated parts of the axis, owing to the repoated cell division and its enlargement, the formation of roots being thus resulted in. 3. At the acid-treated parts, the xylem enlarged in the number of cell layers, owing to the rapid division of cambium cells. Xylem cells became larger and the thickenning and ligniftcation of cell walls were accelerated. The intercellular spaces as well as the irregular, sparse arrangement of cells were observed in xylem. These histological changes, together with some other changes, resembled much to the histological conditions shown at the lower side of the axis held horizontally. 4. Therefore, it may be concluded that one of the causes of the histological differences between the upper and the lower sides of the horizontal axis, lies in the unequal distribution of plant growth-hormones in the axis.
