Abstract
Since little attention has been given to the primordial regions of plants as influenced by X-radiation and chemical growth-promoting substances the author has carried out experiments to determine effects of these agencies on growing points. Snow 1 observed that heteroauxin applied to the growing regions of certain plants caused union of leaf primordia, and Bausor 2 describes the development of root primordia on stems, petioles, and apical meristem when these parts are treated with beta-naphthoxyacetic acid.
In the present study, seedlings of sunflower (Helianthus annuus), zinnia (Zinnia elcgans), and tomato (Lycopersicum esculentum) were given moderate X-ray doses (2300 to 2500 r-units for sunflower and zinnia and up to 3000 r-units for tomato). Plants were stunted, and showed rough, warty, and abnormally-shaped leaves, with fasciation of leaves and of stems and frequent fusion of leaf primordia, as previously reported by Johnson. 3 Often, a few weeks after treatment, the meristematic region was divided into 2 or 3 parts, each with a separate group of primordial leaves, showing that the stem was about to branch. Indole-3-acetic acid (0.5 to 1.0%) applied in lanolin paste to seedlings of the above-named species caused increased growth, and with higher concentrations (2%), a fusion of leaves. The meristematic area either resembles that of untreated controls, or various leaf primordia may become joined, or else displaced from normal position. Colchicine (0.5%) applied also in lanolin paste, was found to retard growth, and it induced development of rough, warty, and misshapen leaves just as X-radiation does, while short,
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