THEORY OF REGENERATION BASED ON MASS ACTION. II

1. Quantitative proof is furnished that all the material available for shoot and root formation in an isolated leaf of Bryophyllum calycinum flows to those notches where through the influence of gravity or by a more abundant supply of water growth is accelerated. As soon as the acceleration of growth in these notches commences, the growth of shoots and roots in the other notches which may already have started ceases. 2. It had been shown in a preceding paper that the regeneration of an isolated piece of stem may be and frequently is in the beginning not markedly polar, but that after some time the growth of all the roots except those at the base and of all the shoots except those at the apex is suppressed. This analogy with the behavior of regeneration in a leaf in which the growth in one set of notches is accelerated, suggests that in an isolated stem a more rapid growth is favored at the extreme ends (probably by a block of the sap flow at the extreme ends) and that when this happens the total flow of ascending sap goes to the most apical buds and the total flow of the descending sap goes to the most basal roots. As soon as this occurs, the growth of the other roots and shoots is suppressed.