RADIUM RAYS 



231 



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 



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 unsuccess- 

 ful, but when a sealed glass tube of radium bromide is suspended hori- 



FiG. 13. 



zontally 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 estab- 

 lished by them in the liquid can not yet be decided. 



