EFFECTS OF RADIUM RAYS ON PLANTS 993 



A few papers not noted in the two reviews of literature cited above 

 may be briefly mentioned here. Hebert and Kling (33), reported that 

 radium radiations appeared to produce no alteration of the atmosphere 

 in which plants were growing. Photosynthesis was not possible under 

 radium rays alone, sunlight being excluded. Respiration and photo- 

 synthesis were considerably diminished in leaves exposed to the radiation 

 before being placed in daylight, but the ratio between oxygen taken in 

 and CO2 given off in respiration was not altered by previous exposure 

 to the rays. 



Acqua (1) reported that certain species are more susceptible to the 

 rays than others. The root systems seem to be more susceptible than 

 the stems and foliage. Some pollen grains appeared not to be affected 

 by exposures that were fatal to others. The movements of protoplasm 

 in such cells as the epidermal hairs of pumpkin, the internodal cells of 

 Chara, and the leaf cells of Elodea canadensis appear to be wholly unaf- 

 fected by exposure to radium rays. Observations of the waiter are in 

 harmony with those of Acqua on this point. 



Fabre (22) exposed unopened flower buds and ovaries of Lilium sp. 

 to rays of different strengths. Buds were arrested in growth and soon 

 dried up; ovaries, stigmas, and anthers were atrophied or retarded; pollen 

 grains had poorly developed nuclei or none at all; pollen grains did not 

 germinate on the stigma; ovules and embryo sacs were atrophied. 



Gertz (27) reported that radium rays completely checked the twining 

 of Cuscuta and the formation of its haustoria. In the same year, Guil- 

 leminot (32) reported that seeds exposed to X-rays of 15,000 M (his unit 

 defined above) and radium rays of 3000 to 5000 M germinate in the same 

 proportions at the end of two years of rest following exposure as at the 

 beginning of the two years of rest. In other words, the injurious effect 

 of exposure persists for two years. Since the seeds were in the resting 

 condition when exposed and for tw^o years thereafter, this result is what 

 might have been expected. 



Gager had shown in 1908 that air containing emanation was injurious 

 to the germination of seeds under the conditions of his experiments, and 

 similar results were reported by Fabre (23) for the germination of the 

 spores of Sterigmatocystis on acid gelatin, using emanation of "high 

 potency." One-half microcurie per cubic centimeter of air retarded 

 germination for the first three days, but on the fourth day the growth 

 of the exposed spores equaled that of the control cultures not exposed. 

 Mucor miicedo was more resistant. There was observed only a retarda- 

 tion of growth with doses below 1 microcurie to 2 liters of air; with larger 

 doses the suppression of the sporocysts. A dosage 1000 times stronger 

 favored the germination of spores on gelatin and the development of 

 the fungal filaments. 



However, Fabre reported that seedlings of Linum caiharticum exposed 

 to emanation in the air of a closed vessel were killed at a strength of 40 



