996 BIOLOGICAL EFFECTS OF RADIATION 



injures (as others had found). Photosynthesis and respiration were both 

 accelerated. Numerous experiments have shown that by exposure to 

 weak radioactivity nuclear and cell division, the development of the 

 plant as a whole, exchange of gases in photosynthesis and respiration, 

 metabolism, flowering and fruiting are all favored by weak and retarded 

 by strong irradiation. The same general conclusion was drawn from the 

 sum total of work cited above in 1908, but by 1914 it had, of course, been 

 more thoroughly documented. 



The effect of radium rays on the germination of seeds was again 

 investigated in 1915 at the Institut Pasteur, Paris. Agulhon and 

 Robert (2) confined their studies to the period when the young seedling 

 was still wholly dependent on the food reserves stored in the seed. First, 

 peas (Pisum sativum) were exposed to such rays as could pass through 

 the thin walls of sealed glass tubes. Second, they were germinated 

 in a solution containing radioactive material. Third, germination was 

 brought about in an atmosphere containing the emanation. In the 

 first case germination was retarded, in the second the results were nega- 

 tive, in the third early growth was accelerated and etiolation resulted. 



After 1915 there were few, if any, papers on the effects of radium rays 

 on plants until about 1920. This hiatus was doubtless due to the World 

 War. G. Hertwig (34) reported that investigations on the effect of the 

 rays of radium and X-rays on algae and fleshy fungi showed retardation 

 of growth, and that the reproductive cells of higher plants were more 

 sensitive than other cells, thus confirming results previously reported 

 (Gager, 25). Pollen grains of a carnation and of Digitalis purpurea 

 would not germinate after exposure. 



The action of buried tubes of radium emanation on neoplasias in 

 plants was investigated by Levin and Levine (44). They found that 

 when a radium emanation tube (of capillary size) is inserted in normal 

 adult tissue, the only perceptible result is the complete destruction of 

 tissue in the immediate vicinity of the tube, owing to the gamma radia- 

 tion. When such a tube was inserted into crown gall tissue the further 

 development of the tissue was inhibited. This is brought about by the 

 inhibition of the nuclear proliferating activity in the tumor cells by the 

 gamma rays. "The tumor tissue in the immediate vicinity of the buried 

 tubes is affected mainly by the soft beta rays. Here, therefore, deeper 

 changes take place in the tumor tissue. Sections of this tissue show the 

 collapse of cell walls radially to the capillary tube, forming a cushion of 

 cellulose. The cells immediately behind this cushion are devoid of 

 both nucleus and cytoplasm. . . . The disintegrated tissue and the 

 cellulose cushion filter off the soft gamma rays. Cells further back of 

 this area are consequently acted on only by the gamma rays." 



In a later paper, Levine (45) reported studies leading to the conclusion 

 that short exposures of crown gall tissue to small doses of radium emana- 



