Page:The Journal of Indian Botany.djvu/390

338 THE JOURNAL OF INDIAN BOTANY. placed to counter-balance, the weight of the piece. Plate II, fig. 27 shows how this was done, and it will be seen that no appreciable curvature took place. In the course of the experiment a lessening of the weight, by loss of evaporated water caused the terminal threads to slacken ; but at the beginning of the experiment, the weight was evenly distributed and the lack of curvature cannot therefore, be due to any pull upwards, at the centre of gravity.

Since the region of curvature is in the weak still unlignified internodes near the apex (vide figs. 1, 2 and 3) it is clear that the bending moment at the point of curvature due to the comparatively heavy, succulent leaves, will be much greater when these are at the apical end, than if they are at the basal (compare figs. 1 and 2 with 3).

In another series of experiments living stems of Coleus still attached to the roots, were laid horizontally, the growing point and the first visible internode, being removed as before. Three pairs of plants were used, and in one of each pair, a pair of apical leaves was left, while in the other one or more near the base. Plate II, fig. 19-26 show the resulting curvature after 24 hours. It will be seen that no definite relationship, can be established between the amount of curvature and the existence or position of leaves Compare Nos. 19 with 20, 23 with 24, 21 and 22 with 25 and 26.

B. The root-forming ' hormones' — Our experiments failed likewise to support Loeb's theory, that root-formation is due to hormones produced in the leaf. Roots were formed freely on the lower side and especially at the region of curvature (figs. 1 and 4) of stems kept damp; but in no apparent relation with the existence or position of leaves. The presence of water, we found to be a much more important factor.

Pieces of stem were placed vertically, in the normal or the reversed position, and one end kept damp, by tying a wet rag round it. In every case roots appeared, whether at the upper or lower end, whether at the apical or the basal. This is exactly in conformity with Klebs results (7).

This occurred also with both isolated and attached leaves of Bryophyllum. Roots appeared always in a day or two, at the parts kept wet. Loeb's results (4) of hanging leaves in different positions, which led him to postulate a flow of root-forming substances towards the base of a leaf appear therefore, to have been accidental. In our experiments, leaves were hung in a vertical plane.

(1) by the petiole

(2) by a hole in the apical end

(3) by a hole at one side and

(4) horizontally by threads through two holes in the lamina.