INTUMESCENCES ON POPLAR LEAVES. II. PHYSIOLOGICAL CONSIDERATIONS

Abstract

In preceding papers (12, 13) the writer has described the occurrence and structure of intumescences on leaves of Populus grandidentata, Populus tremuloides, Eucalyptus coccifera, Eucalyptus cornuta, Hieracium venosum, Mitchella repens, and Thurberia thespesioides. In the present paper an account is given of an attempt to determine the factors involved in stimulating the cells to the unusual growth, which result in these abnormal protuberances. The hypotheses which have been developed to account for the induction of intumescences have been almost as numerous as the records of their occurrence. Sorauer (i8) believed that metabolic disturbance due to an excessive water supply and low assimilation accounted for the outgrowths. In a later paper (I9) he added another factor to the complex, namely, the effect of a high temperature. An excessive water supply due to low transpiration and a high rate of water absorption by the roots, was advanced by Atkinson (I, 2) as the stimulus to formation of oedemas on the tomato and the apple, though he considered that low illumination was favorable also, since it led to the development of weak, watery tissue. Steiner (20) discovered intumescences on leaves of Ruellia formosa and Aphelandra Porteana which he believed were caused by high humidity. By subjecting leaves of Aphelondra to a saturated atmosphere he was able to induce these outgrowths, but he failed to secure them by treating the leaves with copper sulfate, ammonium chlorid, formic acid and various other chemicals; by keeping them in the dark; or by submerging them in water. Douglas (5) induced intumescences on leaves and stems of potato plants by covering them with bell jars. Since the intumescences occurred in either strong or weak light, but not in total darkness, she concluded that light as well as humidity played a part in the abnormal stimulation of the plants. She found also that the abnormalities could be produced by treating young potato plants with copper compounds, as Von Schrenk (23) had previously found in the case of cauliflower. Ktister (i I) secured intumescences on leaves of Populus floated on water in the presence or the absence of light. In strong light, however, the