CUEVATUEE OF BRYOPHYLLUM CALYCINUM. 341
leaves of a plant growing in the ground, which had not grown any roots or shoots in the notches of its leaves, were selected and they were left dipping in water contained in a basin, on the 2nd of December, 1919. Three days later on the 5th of December, roots were found to have grown out from the submerged notches of the leaf, to a length of nearly half an inch. On the 8th December, small shoots also had grown out from the notches.
These observations deny the inhibiting influence of root-pressure and suggest the moist external conditions as accounting for the growth. This is quite in consonance with the fact that the notches in the leaves of the plants had grown out just after a week of heavy rain, although root-pressure must then, presumably, have been considerable, because of the very little transpiration that was possible.
The following experiment appears to be conclusive. A pot plant of Bryophyllam was taken and the stem of the plant was cut off leaving only the last basal node with the two leaves attached. The cut end of the stem was sealed firmly with Canada balsam, to prevent water from being forced out and resulting in a diminution of root-pressure. The axillary buds of both the leaves, were destroyed. One of the two leaves was left dipping in a basin of water so that part of it was submerged. On the 6th day, roots were found to have grown out in clusters from the notches jDf the submerged portion of the leaf. Later on small shoots also appeared. Here if, as seems probable, there was considerable root-pressure, the formation of roots and shoots from the leaf- notches was not in any way inhibited.
Summary
Experiments were made to determine whether special root-forming and curvature-producing substances could be recognised as being formed in the leaves, as assumed by Loeb on the results of his observations on Bryophyllum calycinum. They were in the first instance a repetition of his experiments, but with certain modifications to eliminate the effects of weight. We find no evidence in support of the theory of special curvature-producing hormones, nor of root-forming substances. On the other hand our observations confirm those of Klebs on the effect of an 'excess of water on adventitious root-formation.
A further series of experiments on the effect of the growth of an axillary bud on the development of the marginal leaf-notches, failed to confirm Loeb's results. All differences in the rate and amount of growth of roots and shoots from the margins of the leaf, can in our
