THE ROLE OF WOUNDING AND PARTIAL GIRDLING IN DIFFERENTIATION OF VASCULAR RAYS

The regulation of initiation, size, and spacing of vascular rays was studied experimentally by partial girdling (leaving a longitudinal narrow bridge) and small wounding removing 1-2 cm2 of bark in mature stems of Pinus halepensis Miller and Ailanthus altissima Swingle. The partial girdling treatment, which. increased cambial activity locally, increased the number of xylem rays and the width or height of some of the existing ones. In addition, it caused the formation of resin ducts in P. halepensis and gummosis in A. altissima. Similar results were obtained with longitudinal wounds, even when growth was not confined to narrow bridges of cambium, and without changing mte of cambial activity. In both cases, within a narrow bridge and near a wound, the increase in ray number and ray dimension was mainly a wound response, but ray size was sometimes larger near the wound surface than in the middle of the narrow bridges.