EFFECTS OF RADIUM RAYS ON PLANTS 1003 



after the removal of the source of radiation, the fungus resumed its 

 normal rate of growth. 



That photosynthesis may be stimulated by beta and gamma rays 

 was also reported by Stoklasa (80). Cucumber plants whose leaves 

 were treated yielded, in his tests, 1243 gm. as compared to 689 gm. for 

 the control plants. Exposed mint and tobacco plants weighed 527 

 and 684 gm., respectively, as compared with 396 and 316 gm. for the 

 controls. 



Chondriosomes were found to be more resistant to beta and gamma 

 rays than the nucleus, according to Milovidov (51). In roots of Pisum 

 sativum, irradiated for 0.5 to 2 hr., there were irregular mitoses, but the 

 chondriosomes appeared to be normal. After exposure for 5 to 6 hr. 

 many mitochondria appeared much swollen, but others were not altered. 



In 1930, ]\Iilovidov reported experiments confirming his earlier 

 results and showing, besides, that the elements of the chondriosome in 

 Saprolegnia, which appear inactive, are very resistant to the beta and 

 gamma rays, showing no change after an irradiation for 5 hr. or more 

 to rays from 5 mg. of radium chloride contained in a sealed glass tube. 

 They behave quite like the mitochondria of the higher plants. 



Feichtinger (24) analyzed the action of alpha and beta rays by using 

 polonium and radium on rootlets of Crepis virens. The alpha rays 

 produced injury to a depth of 30//; the tissues lying deeper than that 

 appeared normal. The beta rays damage the tissues throughout the 

 entire diameter of the root, owing to their greater penetrability. 



In 1930, Stoklasa (83) and four collaborators review a great deal of 

 the previously published work, and give an extensive bibliography. 

 They discuss the effects of exposing seeds to beta rays only, beta and 

 gamma rays together, and pure gamma rays. From their own experi- 

 ments, they conclude that 18 to 24 hr. is the most favorable duration 

 of exposure of seeds. A longer exposure to either beta, beta and gamma, 

 or pure gamma rays is injurious. When seeds^ are exposed to high 

 concentration of the emanation, the result is injurious to germination. 

 The toxic effect of strong radioactivity on the seeds of forest trees is 

 increased by ultra-violet light. When the radioactivity is of the strength 

 50,000 to 150,000 ME, the germination of seeds of Pisum sativum, 

 Pisum arvense, Lupinus angustifolius, Vicia Faba, and others is stimulated. 

 At 200,000 ME the intensity of germination is somewhat diminished 

 and increasingly with increase in the strength of the radiation. At 500,- 

 000 ME the germination of some seeds (e.g., Trifolium pratense and 

 Hordeum distichum) is completely inhibited and the embryo killed. 

 Forest seeds appear to be more resistant than others. Other experiments 

 prove that the photosynthetic processes are favored by beta and gamma 

 rays together and by pure gamma rays; the elaboration of new living- 

 plant substances is also favored. 



