Indol-3-ylacetic acid (IAA), gibberellin A3 (GA) and 6 benzylaminopurine (BAP) were applied factorially each at 3×10−2 M in lanolin to the roots and stems of Sitka spruce seedlings and the activity of the two secondary meristems, the vascular cambium and phellogen, and of the parenchymatous tissues between them, was examined. All the treatments, with the exception of GA produced a localized stimulation of radial growth at the point of application and there was a similarity in the response of the various tissues in both the root and stem. Radial growth of the xylem was not significantly affected in the roots whereas in the stems BAP and IAA stimulated growth. In the phloem BAP produced significant stimulation in both roots and stems and IAA stimulated growth in the roots. Growth of the parenchyma and periderm external to the phloem was also strongly stimulated by both BAP, and IAA in roots and stems. In roots and stems the application of BAP altered the derivatives produced by the vascular cambium, resulting in the production of large multiseriate rays in the xylem, and giving rise to an overall increase in the proportion of ray tissue.
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Philipson et al. (1980) studied this question.