Page:The Journal of Indian Botany.djvu/392

340 THE JOURNAL OF INDIAN BOTANY. From this we may conclude that neither the stem itself, nor the opposite bud, nor the axillary bud, exert any absolute inhibition, on the development of the marginal notches, and probably affect it very little.

D. Regeneration in leaves still attached to the living plant. — Several normal, erect, healthy plants of Bryophyllum were found in which roots and shoots had arisen from the notches of several leaves in contact with the parent plant. It should be mentioned that the preceding week had been a very rainy one. Most of the leaves jvhich had grown shoots at their notches were found to be of a slightly paler green colour, but there were also several green leaves among the number. In none of these stems had the terminal buds been injured or destroyed and they were growing quite well. In the case of one plant where the terminal bud, had been accidentally destroyed, the notches in the leaves had not grown out, but the axillary bud lower down, was starting to grow. The stems of all these plants were quite erect and to all appearance normal. There was no indication of their roots having been injured or of any other pathological condition as suggested by Loeb in his objection (5) to Miss Lucy Braun's very similar observation.

Loeb, indeed contended (l) that "when these leaves are attached to the stem of the whole plant, in the natural condition, they never produce roots and shoots in their notches." The chief factors which he mentions, as tending to prevent the formation of roots and shoots on the leaves when in the natural condition, are (l) the growth of buds on the main stem and (2) root-pressure. His explanation is that the formative materials which are required for active growth, are constantly flowing to the terminal bud from all the other parts of the plant and hence the notches in the leaves have no chance of growing. This explanation does not, however, apply to the instances cited above, as in all those cases, the terminal buds on the main erect stems were quite healthy and active.

Turning now, to the second factor that Loeb mentions, he says that the presence or growth of roots on the main stem inhibits the growth of notches in the leaves because. of root-pressure.

It is difficult to conceive how root-pressure can inhibit growth in the notches of the leaf, and Loeb does noc explain how it does. In the concluding passages of his paper (l), he says that attempts to induce growth in the notches of the leaves proved futile. He says " the writer left several leaves of the plant submerged in water for months without any results ", and therefore concludes that root- pressure is the inhibiting factor.

yith a view to find out, whether this was really the case, three