64 NEUTRON EFFECTS ON ANIMALS 



(Fig. 3) was taken a little later when the laterals were just beginning to 

 appear in the lower energy group. 



In the groups receiving 2000 n, the average length of the primary roots 

 at the time of death was 31 mm. in the lower energy neutron group while it 

 w'as 35 mm. in the fast neutron group. This difference in sensitivity is 

 amplified when the record of the laterals is considered: 119 hours after 

 germination 21 per cent of the fast neutron group had laterals, while none 

 had appeared as yet in the lower energy group; 28 hours later, the former 

 group had 100 per cent laterals, and laterals had appeared in 32 per cent 

 of the latter group. 



The difference in the effects of the two qualities of neutrons on adven 

 titious roots of seedlings which had received doses from 2000 to 5500 n 

 can be seen in Table I. While reduction in average length was nearly the 

 same after both ciualities of radiation, the lower energy neutrons signifi- 

 cantly reduced the percentage of seedlings producing these roots. 



The differences in effect of the two qualities of radiation may possibly 

 have been due to a greater sensitivity of the 100 r chamber to fast neutrons. 

 If this was true, the material radiated with lower energy neutrons would 

 have actually received a greater dosage. No experiments have been done 

 and no evidence was found in the literature that makes it possible to evalu- 

 ate this hypothesis. 



Other workers have found indications that living material is more sensi- 

 tive to lower energy neutrons than to fast neutrons. Jennings and Garner 

 (11) found evidence of this specific sensitivity in the case of certain bacteria. 

 Stone (12) reported that to produce a minimum threshold skin reaction, 

 larger doses were required when fast neutrons were used than when lower 

 energy neutrons were used. 



If the sensitivity of the 100 r chamber is the same for both qualities of 

 neutrons, the results obtained with corn indicate that lower energy neu- 

 trons are more effective in retarding various phases of root development 

 than are fast neutrons. 



SUMMARY 



1 . Neutron radiation of dry seed of Zea mays affected the length of the 

 primary root, the time of appearance of lateral roots, and the character 

 of the adventitious roots. 



2. Each type of response to radiation showed best within its own special 

 range of dosage. 



3. Small doses of fast neutrons appeared to have some stimulating effect. 



4. Adventitious roots were more damaged by lethal doses of X-rays 

 than by lethal doses of neutrons. 



5. Corn seedlings were affected more by lower energy neutrons than by 



