Dixon & Wigham — Radiations from Radium Bromide. 179 



the tube, but no curvatures were apparent. The seedlings, how- 

 ever, within about 1 cm. radius, were slightly less grown than their 

 fellows ; but this difference was by no means marked, nor did 

 they appear unhealthy or in any way abnormal. At the end of 

 ten days, the difference in height of the seedlings close to the 

 radium, and of those further removed, was more noticeable ; and 

 while the average height of the peripheral plants was 51 mm., that 

 of those within the 1 cm. radius was 44 mm. 



The radium-tube was then removed, and the seedlings exposed 

 to daylight. The central plants still remained behind the others 

 in point of growth for the few days during which their develop- 

 ment was watched. 



Experiment II. — Seeds similarly treated and similarly exposed 

 to the radiations showed, three days after germination, the same 

 slight retardation of growth. In this case it was noticed that the 

 number and development of the root-hairs of the retarded seedlings 

 were considerably inferior to those of the others. But otherwise 

 the retarded individuals seemed healthy. Microscopic examination 

 of their cells did not reveal any perceptible difference from those of 

 the unretarded plants. 



Experiment III. — In order that the radiations might act on 

 the seeds throughout germination, dry seeds were distributed over 

 moist sand. The radium-tube was supported so that only the 

 thickness of the glass (about 0*5 mm.) intervened between it and 

 the test of the central seed. Notwithstanding this close proximity, 

 the central seed and its fellows had protruded their radicles on 

 the second day after sowing. As before, a slight retardation 

 of growth was observed in the subsequent development of the 

 central seedlings, but no injuries could be made out. Further, 

 there were no curvatures induced by the radiations. 



In order to test a motile organism for radiotropic response, 

 Volvox globator was selected as suitable material. Several hundreds 

 of this colonial protococcoid were used in the experiment. A test 

 by illumination with feeble daylight showed that the material 

 was positively photoscopic. The colonies were then enclosed along 

 with the radium-tube in a test-tube quite filled with richly 

 oxygenated water, taking care to include no visible air-bubbles 

 with it. By this precaution the chemiotropic influence of air- 

 bubbles was avoided, while the organisms were not rendered 



