Chapter 7 



EFFECTS OF NEUTRONS ON EARLY ROOT DEVELOPMENT OF 



ZEA MAYS 



By MARY A. RUSSELL and JAMES U. GARXER, Jr. 



Most of the work describing the effect of neutrons on plant material 

 compares these effects with those produced by X-rays or other forms of 

 radiation. Marshak (I) and Thoday (2) discussed the comparative effect 

 on chromosomes, Zirkle et al. (3) dealt with the growth of wheat seedlings 

 and fern spores, and Gray et al, (4) determined the doses of four different 

 types of radiation which killed young bean plants. The following investi- 

 gations were made to determine the sensitivity of various parts of the root 

 system of corn (Zea mays) to neutrons. 



The corn seed was ''Patriot Hybrid No. 52" furnished by the Seaboard 

 Seed Co. Although preliminary experiments showed that the seed was 

 much more sensitive to neutrons when it was germinated than when dry 

 (as is the case with X-rays (5)), the seed was radiated Avhile dry in order 

 that large doses might be built up by exposure to neutrons over a period of 

 several days. During radiation the seed was held by glass test tubes in- 

 serted in lead cylinders. Each tube had a capacity of about twenty-five 

 kernels. After radiation, control and treated seed was soaked for thirty 

 minutes in a 0.05 per cent aqueous solution of mercurophen to prevent the 

 growth of mold, then placed between layers of damp paper towelling in a 

 large moist chamber. After about forty-eight hours in an incubator at 

 30°C. the primar}^ roots were measured. The seedlings were then placed 

 in jars of moist sphagnum moss with the roots arranged around the edge 

 so that they could be observed through the glass. These jars were kept 

 in the dark except when they were removed from the incubator for ob- 

 servation of the seedlings at twelve to twenty-four-hour intervals. 



Fast neutrons (6) were used in all experiments unless otherwise specified. 

 The fast neutrons, with an average energy of about 6 MEV, produced 

 by the cyclotron, were utilized by placing the corn in their path, as shown 

 by position 8 (6, Fig. 1). Lead cylinders, with walls one inch thick and 

 with one-inch lead plugs in the ends, were used as gamma ray filters. 

 Intensity measurements were made Avith Mctoreen r meters in the cyUnders 

 as described by Enns et al. (G). 



In order to obtain information concerning the intensity of gamma radia- 

 tion within the cylinders, additional measurements were made with two 

 inches of lead between the cylinders and the beryllium target of the cyclo- 



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