1066 BIOLOGICAL EFFECTS OF RADIATION 



duction in a "moistened" but not germinating condition "2 days after 

 radiation." Although the power to germinate was decreased by the 

 treatment, the production of CO2 was increased. This acceleration must 

 not be granted much emphasis, however, because it may not have been 

 a direct result of radiation. It might well have been an indirect effect 

 due to increased rate of entry of water through the irradiated seed coats in 

 comparison with the absorption of water by the control seeds. The seeds 

 were not thoroughly soaked in water and a small difference in water 

 content at that point would account for a great difference in rate of 

 respiration. 



The length of exposure to the radium, the quantity and nature of the 

 radium salt used, the time required to measure the respiration after 

 moistening the seeds, and similar details of the experimental procedure 

 are wholly lacking in the report of results. The fact that germination 

 was decreased to at least 25 per cent of that of the control seeds indicates 

 a powerful action on the seed embryos, but the rate of respiration at any 

 time after irradiation does not seem to have been fairly measured. 



The best and only thorough study of the influence of beta particles on 

 plant respiration is that by Reich (17) reported in 1926. He used 

 chiefly dry seeds of Pisum which were exposed for various time intervals 

 to the radiation from 5 mg. of radium chloride in a glass tube held 

 8 mm. from the seeds. The meristem of each embryo was turned toward 

 the radium except in a few tests for exposure from the rear. After 

 irradiation, the seeds were soaked in water for 18 to 24 hr. and their CO2 

 production was then measured at intervals of 5 to 7 hr. for the next few 

 days, with the ruptured seed coats removed. In the few tests with seeds 

 soaked before irradiation, the results were the same except that shorter 

 exposures were required to produce the same results as in dry seeds. 



The conclusions from these extensive tests, which also included 

 measurements several months after irradiation, were in favor of a marked 

 depression in respiration. This injurious effect became even more pro- 

 nounced with a lapse of time during which the seedlings continued to 

 grow. Dry seeds were found more resistant to exposure than soaked 

 seeds. The cotyledons were influenced slightly but the principal effect 

 was felt by the rest of the embryo. 



A temporary acceleration which was in evidence for a few days was 

 obtained with exposures of 2 hr. or less. For exposures under 3^^ hr. and 

 with dry seeds, the preliminary accelerations of from 1 to 50 per cent later 

 disappeared to leave the respiration rate normal for the next few days. 

 With exposures of over 1^ hr., a depression in rate eventually appeared 

 and its extent was in proportion to the length of the exposure. 



It must be emphasized again that these conclusions for radium 

 radiations, with the alpha particles eliminated and with little or no 

 effect from the gamma rays, are only qualitative. Moreover, they are 



