CURVATURE OF BRYOPHYLLUM CALYCINUM. 339
In every case provided the atmosphere was kept saturated, roots appeared with apparently equal facility at any notch.
G. Regeneration. According to Loeb, the growth of roots and shoots', at the marginal notches of a leaf is ordinarily inhibited, by suction of the stem and especially of the growing axillary buds. To verify this : —
(1) A piece of the stem of Bryophyllum had one leaf at the basal portion alone left, and it was left in a moist chamber supported in the horizontal position on a board. On the 7th day (Plate I, fig. 11) roots had grown out from the notches of the single leaf, and the opposite bud showed signs of growth. On the 14th day, the bud opposite the basal leaf had fully grown out and several shoots also had appeared from the notches of the basal leaf. Roots had also appeared from the under-side of the basal node.
Now, if really the opposite bud inhibited the growth in the notches of the basal leaf, one would expect that as the opposite bud began to grow, the roots that had grown from the notches of the basal leaf would not have developed any further. On the contrary, they continued to grow, and shoots also appeared from the notches. In short, the growth in the notches of the leaf, progressed side by side with the growth of the opposite bud. Hence, apparently no inhibi- tion had taken place.
(2) Two pieces of the stem of Bryophyllum, containing each a single node with only one leaf attached were suspended so that part of the lower leaf was sub-merged in water. After 10 days, it was found that the submerged notches of the lower leaf, in each case, had developed roots, while the opposite bud also was developing. (Plate I, figs. 12 and 13).
(3) A piece of the stem of Bryophyllum containing a single node with two leaves attached was arranged so that one of the leaves had a part submerged in water. On the 6th day roots were found to have grown out from the notches of the submerged lower leaf. On the 9th day the bud in the axil of the submerged leaf, as well as the bud in the axil of the opposite leaf had developed. The upper leaf withered and finally fell off, and is therefore not seen in the photo- graph (Plate I, fig. 18). A root had also grown from the piece of stem.
In this case again, if Loeb's inhibition theory were correct, one would expect that since each of the axillary buds inhibited the development of the opposite leaf, none of the two leaves should have grown any roots in their notches. As a matter of fact, the lower submerged leaf produced roots in its notches and its opposite bud also developed, as also the other axillary bud.
