The Nature of the Directive Influence of Gravity on the Arrangement of Organs in Regeneration. by Jacques Loeb

In preceding papers it has been shown that gravity has a directive influence on the arrangement of certain organs in the regeneration of Bryophyllum calycinum. Thus, when an excised piece of stem of Bryophyllum is suspended horizontally in moist air, roots will grow abundantly on the lower side of the stem but not on the upper side, with the exception of the basal end where the roots will grow on both sides. In order to get abundant root formation it is necessary to preserve one of the apical leaves on such a stem since the leaf furnishes most of the material for the growth of the roots, t A second case in which this directive influence shows itself is the leaf of the same plant. When we suspend an isolated leaf of Bryophyllure (in moist air) sidewise, in a vertical plane, roots and shoots will grow abundantly in the notches of the lower side, but less abundantly and frequently not at all in the notches of the upper side of the leaf (Fig. l, upper row). This phenomenon was explained by the writer in the following way. Gravity causes a slightly greater collection of sap on the lower side of the organs mentioned and this causes the dormant buds for root formation to grow out a little earlier or more quickly on the lower than on the upper side of the stem or the leaf. I t is a general rule in the phenomena of regeneration in Bryophyllum that organs which grow out first or more quickly attract for some reason the flow of sap (possibly by modifying the direction of the sap flow) and thereby inhibit or retard the growth of similar organs in other places, and this inhibitory factor is added to the influence of