Responses of Pea Roots to Application of Certain Growth-Regulating Substances

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Abstract
Characteristic changes in certain tissues follow the application of some growth substances in lanolin to roots of Pisum sativum seedlings. Application of asparagine, indoleacetic acid, or 2,3,5-triiodobenzoic acid has little effect. Changes were very marked following the treatment of uncut roots with tryptophane or with 2,4,5-trichlorophenoxyacetic acid, or of cut roots with the latter substance. Following application of tryptophane, an increase in the root diam. was brought about by proliferation chiefly of cambium and xylem parenchyma. Some divisions occurred in the pericycle, a few in the endo-dermis. Scattered cells in the stelar region matured as sca-lariform tracheids. Effects visible in pea roots treated with 2,4,5-trichlorophenoxyacetic acid were increase in root diam., especially near the tip, brought about by increase in the number of cells with no marked enlargement of cells; stretching and tearing of cortical cells in the enlarged part of the root; hypertrophy of epidermal cells; increase in the number of root hairs; and cessation of maturation of vascular tissues. There was active division of the cortical parenchyma cells near the meristematic region of the root, and some proliferation of en-dodermal cells was evident, but most of the meristematic activity was in the pericyclic region. The pericyclic proliferation occurred in a complete ring near the root tip; at higher levels of the root it appeared largely opposite the xylem arms and was limited in the mature region to the vicinity of young branch roots.