NEUTRON EFFECTS ON ANIMALS 



61 



with X-rays. When one group of corn seedlings radiated with 600 n was 

 compared ^\ith another radiated with 6000 r, it was found that the neutrons 

 caused retardation in the length of the primary roots and delay in the 

 appearance of the laterals, while there was no appreciable difference between 

 the X-rayed seedlings and the controls. This indicates a neutron to X-ray 

 ratio of less than unity, as was also found by other authors including Zirkle 

 (t aJ. (3) who used wheat seedlings and drosophila. 



Observation of the adventitious roots was useful in the study of differ- 

 ences between the effects of fast neutrons and lower energy neutrons 

 (Table I). A difference appeared when a comparison was made between 

 the percentages of adventitious roots which were present after radiation 

 doses of 2000-5500 n. With doses near such a level no lateral roots ap- 



TABLE I 



Effects of Fast Neutrons and Loirer Energy Neutrons on the Adventitious Roots of Corn 



Seedlings 



peared at any time, and measurements of the primary roots showed little 

 difference between 5500 and 80,000 n. 



Effects on Lateral Roots. While the effects of neutrons on adventitious 

 roots were apparent after comparatively large doses, the lateral rootlets 

 growing out from the primary root indicated the neutron sensitivity within 

 the range of about 100 to 2000 n. ]\Iartius (9) found that the difference 

 between the time of appearance of lateral roots on controls and on X-rayed 

 bean seedlings was proportional to the amount of radiation. Russell (5) 

 found this to hold true for corn seedlings. There is apparently a tendency 

 for the laterals on normal seedlings to appear when the primary root has 

 reached a certain length. 



A preliminary experiment was undertaken to investigate the possibility 

 of stimulating plant growth by small doses of neutrons. Kersten et al. (10) 

 had been able to stimulate corn growth with low doses of X-rays. Three 



