STIMULATION OF GROWTH OF SOY BEAN SEEDS BY SOFT X-RAYS

Abstract

In recent years the effect of x-rays on the growth of seeds has been the subject of considerable investigation. Most of the work has been done with the Coolidge tube which, at the voltages commonly employed, produces chiefly hard, or short wave length x-rays, with only a small percentage of the energy of the radiation in the soft, or long wave length region of the x-ray spectrum. The injurious effect of large doses of any x-ray wave length seems established without contradiction, but the effect of small doses seems doubtful, producing sometimes stimulation as found by Doroshenko (4), Ingber (7), Johnson (8), Nikitin (15), Snyder (16), Shull and Mitchell (17) ; and again injury and retardation as found by Ancel (1), Cattell (2), Delone (3), Francis (5), Goodspeed (6), Johnson (10), Lallemand (12), Malhotra (13), Moore and Haskins (14). Greater stimulation was indicated when a filtered x-ray beam was used than when the x-rays were unfiltered in the work of Nikitin (15), and Shull and Mitchell (17). Filters, such as those used in the experiments, reduce the intensity of all wave lengths but diminish the soft part of the spectrum preferentially so that if stimulation is obtained it may be attributed to the short wave length part of the x-ray spectrum and injury to the long wave length part, or, stimulation to the low intensity and injury to the high intensity, regardless of the wave length (17). Since no experiments have been reported in which only soft x-rays were used to irradiate large numbers of dry seeds, it was thought desirable to carry out an experiment in which dry seeds were irradiated with only the soft part of the x-ray spectrum, and in which the effect of abnormal conditions upon the results was minimized by growing a large number of plants from irradiated and control seeds in permuted rows in the open field under natural soil and weather conditions.