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XIX. 



PRELIMINARY NOTE ON THE ACTION OP THE RADIATIONS 

 FROM RADIUM BROMIDE ON SOME ORGANISMS. 



By HENRY H. DIXON, Sc.D., Assistant to the Professor of Botany, 

 University of Dublin ; and J. T. WIGHAM, M.D., Assistant 

 to the Lecturer in Pathology in Trinity College, Dublin. 



(Plates XVI.-XVIII.) 



[Read, December 15 ; Received for Publication, December 18, 1903 ; 

 Published, March 12, 1904.] 



Last autumn one of us began experimenting on the effect of 

 these radiations on plants. The experiments were made on seed- 

 lings of Lepidium sativum and on Volvox globator. They were 

 planned so as to find out if the radiations would act as a stimulus 

 to evoke growth-curvatures, or if they would exert a directive 

 action on the motion of a motile organism. At the same time, 

 abnormal and pathological effects were looked for. 



The experiments carried out on the seedlings were as follows : — 



Experiment I. — 100 seeds of Lepidium sativum were uniformly 

 distributed over an even surface of moist quartz sand. After 

 germination had taken place and the radicles were just visible, 

 a sealed glass tube containing 5 mgrs. of radium bromide 

 was set over the central seed at a distance of 1 cm. from it. In 

 order to remove the disturbing effects of uneven illumination, and 

 to render the seedlings as sensitive as possible to the radiations, 

 they were kept in the dark, except for the feeble light emitted by 

 the radium bromide itself. 



Thus arranged, if the seedlings were positively radiotropic — i.e. 

 tended to turn to the source of the radiations — the central plants 

 would grow vertically upwards, while those nearer the periphery 

 of the sand would incline towards the centre. If, on the other 

 hand, they were negatively radiotropic, they would all be deflected 

 from the radium-tube to a greater or less degree, according to the 

 vigour of the response. 



At the end of a few days the seedlings had grown up round 



