1064 



BIOLOGICAL EFFECTS OF RADIATION 



but one of these measured the O2 consumption and the other followed the 

 production of CO2. Thus their results are supplementary and practically 

 identical and together form a sound basis for belief in a depressant effect 

 on the respiration of higher plants, at least. 



Miss Johnson (6) used seeds of Helianthus annuus before they had 

 lost any great amount of their water, which was found to be 58.7 per cent 

 of the weight of the seeds. She found it necessary to use doses of from 

 1 to 5 H.E.D. to affect the seeds, of 10 H.E.D. to inhibit growth to any 

 extent, while a 20-H.E.D. dose on the seeds produced seedlings which 

 died just as the cotyledons started to emerge from the soil. Higher 

 doses of 24 and 40 H.E.D. were used in the tests for which the changes in 

 respiration were measured. The following is the result of one experi- 

 ment while only four experiments in all were performed: 



Table 2 



The experiments conducted by Bersa (1) were numerous, the technique 

 accurate, and the evidence is convincing. The seeds used were those of 

 Vicia Faba and the exposures of from }i to 2 H.E.D. were made on good 

 seeds soaked in water for two days by which time they had burst their 

 seed coats. The tests for respiration, as measured by oxygen consump- 

 tion, were made on the excised root tips removed in small lots at certain 

 intervals. Doses of ^i H.E.D. had no effect on respiration. In most of 

 the experiments the dose was 1 H.E.D. and in Fig. 2 there is given a com- 

 posite graph to show its effect on the rate of respiration of primary root 

 tips for hours after the seeds were irradiated. 



The dotted lines indicate, by their distances from the solid line, the 

 probable errors of the measurements which showed decided fluctuations, 

 especially for those made after 2 or 3 days. 



The difference in these results for higher plants, in comparison with 

 the influence of X-rays on lower plants as represented by yeast, must be 

 left without explanation until more evidence has been produced. The 

 conclusions for the influence on the higher plants seem to be based on 

 better developed evidence, if anything, than that for the lower plants, 

 which have been represented only by yeast and this is hardly typical of 

 the group as a whole. If assumptions must be made concerning the 

 metabolism of an untried plant, it would appear to be safer to expect a 



