Page:Popular Science Monthly Volume 74.djvu/235

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grown from exposed seeds were still sensitive to gravity and unilateral illumination, and the experiments of the writer confirm this result. Under certain conditions of exposure of corn grains, however, the seedlings failed to respond to gravity, and grew horizontally, close to

PSM V74 D235 Radium bromide may effect gravity effect on seed growth.png

Fig. 12.

the soil surface. Thus, in one experiment, the grains were exposed for twenty-seven hours to rays from radium bromide of 1,800,000 activity, and all of them showed this tendency to a greater or less degree (Fig. 12, pot 27). Whether geotropic sensibility was destroyed by the exposure is difficult to say, for histological examination showed the tissues to be so abnormal that it is possible the plants could not have stood erect even if they had been able to detect the stimulus of gravity.

All attempts to obtain a curvature of growing organs or plants toward or from a radium tube or radium-coated rod proved unsuccessful, but when a sealed glass tube of radium bromide is suspended horizontally

PSM V74 D235 Plant roots curve towards radium source of 5mm distant.png

Fig. 13.

in tap-water, or in nutrient solution, in which radicles of white lupine seedlings are growing vertically, the tips of the roots may be made to curve toward the radium. Such a result is illustrated in Fig. 13. In this experiment the radium tube was originally about 5 mm. distant from the root-tips. Whether this result was due to the direct influence of the rays, or to some undetermined condition established by them in the liquid can not yet be decided.