6/\. PREVIOUS INVESTIGATIONS UPON PLANTS 



Dorn, Baumann, and Valentiner,^^ experimented with the gase- 

 ous emanation, and found that Bacillus typhosus, cholera germs, and 

 bacilli of diphtheria, exposed to its influence, were killed. The 

 effects were attributed to the /9 rays * given off by the emanation, 

 and not to the gas itself, apart from its radioactivity. 



In August, 1905, were published Koernicke's*'' further researches 

 concerning the effect of Rontgen and radium rays on plants. His 

 earlier results were confirmed by these experiments, in which he used 

 0.75 gm. of about 4 per cent, radium-barium chloride in a thin 

 aluminium and glass capsule. Brassica was found very resistant, 

 and no difference was noticed in the effect of rays from the large 

 quantity of radium preparation passing through thin aluminium, and 

 of those from the smaller amount in the thicker glass capsule. The 

 growth of roots of Vicia Faba was inhibited, and, in some instances, 

 was resumed after the radium was removed, in other cases not. The 

 shoot, once inhibited, never resumed growth, but luxuriant adventive 

 sprouts developed in the axils of the cotyledons. Tissues were made 

 brown by the exposures, and marked individual variations were found 

 in the behavior of the seeds of Vicia. The growth of Pisum seed- 

 lings was retarded in proportion to the length of exposure of the seed 

 before germination. 



These experiments indicate that roots are more sensitive than 

 shoots, and, in the light of Willcock's and of Hertel's work, this was 

 explained by the presence of chlorophyll in the shoots. All attempts 

 to affect the geotropic sensitiveness of roots and shoots were unsuc- 

 cessful, except in those cases where growth had been completely in- 

 hibited by the rays. Starch was not found in roots or shoots of 

 seedlings grown from the seeds exposed for two days before planting. 

 Exposure to X rays gave similar results. Exposed seedlings also 

 responded phototropically to light so long as they were growing, but, 

 says Koernicke, " at the conclusion of growth they were in a condi- 

 tion which I may designate as ' radium-rigor and Rontgen-rigor.' " 

 The light waves coming from the preparation induced phototropic 

 curvatures in sporangiophores of Phycomyces nitens after an expo- 

 sure of about 15 hours, at a distance of more than 3 cm. This re- 

 sponse failed when the light rays were cut off by wrapping the 

 radium tube in black paper, and Kornicke feels sure that the result 



* So the authors. The emanation, however, does not give off /3 rays, but only a 

 rajs. See p. 9. 



