NETTROX EFFECTS ON ANIMALS 59 



tron. The readings of the r meter were shghtly lower when the acUUtional 

 two inches of lead were used, indicating the presence of some gamma 

 radiation even when the c^'linders were used. To determine how much 

 consideration should be given to the possible effects on dry corn of the 

 small amount of gamma radiation present in the lead cylinders, a sample 

 of corn was irradiated with 92-Kv. X-rays for a total dosage of 6000 r. 

 Following germination no measurable effect was observed. Since X-rays 

 are similar to gamma rays, and the gamma radiation received by the corn 

 in these experiments probably would not exceed 6000 r, any possible effect 

 of gamma rays was not considered. 



Lower energy neutrons were obtained by putting the seed in lead box 7 

 (6, Fig. 1). Neutrons reaching this position had an average energy of 

 about 2 or 3 MEV, as explained by Enns cl al. (6). 



Effect on Primary Roofs. When low doses of neutrons were used (53- 

 160 n), there was a slight indication of possible stimulation based on the 

 comparison between the length of the primary roots and those of the con- 

 trols. Growth of the primary root was retarded by doses of 200 n and 

 over (Fig. 1). When 2000 n were used, the seedlings died after about 120 

 hours of slow growth, after doses above 2000 n they died within 72 hours, 

 with less growth of the root. Circumstances prevented our using doses 

 of over 80,000 n, but it is hoped that at a future time the dose of neutrons 

 required to prevent germination may be determined. The fact that doses 

 between 5500 and 80,000 n resulted in delayed killing after a definite and 

 similar amount of growth suggests an effect comparable to results obtained 

 by Collins and ]\Iaxwell (7) when they X-rayed dry corn. They found 

 that "from 60,000 to 100,000 r units the percentage of germination re- 

 mained unimpaired but all the plants died in the seedling stage", and from 

 their other experiments discovered that doses of approximate!}^ 2,000,000 r 

 completely prevented germination. 



Effects on Adventitious Roots. While differences in the response of the 

 primary root to various amounts of radiation seem to be the most obvious 

 and the easiest to measure, the response of other parts of the root system 

 have real significance. The normal corn seedling raised under the con- 

 ditions of these experiments produced four adventitious roots at the first 

 node of the shoot. The average length of each of these roots was about 

 40 mm. when measured 100 hours after germination started. The adven- 

 titious roots of seedlings which had received 1000 n or less showed no differ- 

 ences as compared with the controls, but doses of 2000 n and over produced 

 damaging effects as shown in Table I. Smith and Kersten (8) report that 

 after dry corn received a dose of soft X-rays sufficient to kill the seedlings 

 after their primary roots had reached a length of 30 mm., no adventitious 

 roots were present. A dose of 80,000 n still permitted the appearance of 



