972 BIOLOGICAL EFFECTS OF RADIATION 



of the same species react in a different manner according to the individual 

 differences in the seeds and to the stage of development. Soaked or 

 germinating seeds are more susceptible to the rays than dormant ones. 

 Series of lighter doses seem to have less biological effect than has the 

 same dose given all at one time. More investigations on the influence 

 of temperature on the effects of radiation and on the alleged forcing of 

 buds by the rays are needed before definite conclusions can be drawn. 



EFFECT ON RESPIRATION 



Preliminary experiments by Shull and Mitchell (60) indicate that 

 very weak doses cause increased respiration in rayed seedlings. Bersa 

 (76) and Johnson (19) have both found reduction in respiration when 

 medium to heavy doses were given. Bersa found that in excised root 

 tips given a dose of 5 H, ^ to 1 hr. after irradiation, there occurred a 

 transitory, weak acceleration due to a temporary, traumatic effect of the 

 stimulus; 6 hr. after irradiation, however, the respiratory rate was lower 

 than that of the controls. Joluison found that depressed respiration 

 accompanies inhibited growth of the sunflower resulting from heavy 

 irradiation. 



EFFECT ON PLANT MOVEMENTS 



Kiister (34) has given information concerning the effects of radiation 

 on the nyctinastic and seismonastic movements in the bean and in 

 Mimosa. His results are contradictory to those of Seckt (59) who found 

 that radiation caused a folding of the leaflets of Mimosa and Oxalis. 

 Kiister, in numerous carefully controlled experiments, produced perma- 

 nent paralysis in both Phaseolus vulgaris and Mimosa by exposing the 

 bases of the petioles and bases of petiolules to the rays. The leaves were 

 paralyzed only to the extent that the rays had touched them. The 

 action of the pulvinus at the base of the leaflets was not influenced by 

 the paralysis at the base of the leaf. This may be shown by the fact 

 that the stream of sap which flows through the paralyzed pulvinus con- 

 tinues up to the leaflet. Hard rays were found to be more effective in 

 producing paralysis than soft ones. No difference was found in the plant 

 response when exposures were made at different hours; those exposed 

 in the early morning responded similarly to those exposed at noon or in 

 the afternoon. Aside from paralysis, the plant was uninjured; blossom- 

 ing and fruiting occurred normally. 



SUMMARY 



The evidence presented in the papers dealing with the physiological 

 effects of X-rays indicates the injurious effects of medium and heavy 

 doses. The problem of the so-called stimulative action of light doses, 



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