966 BIOLOGICAL EFFECTS OF RADIATION 



an indirect benefit from irradiation, as they show extraordinary elonga- 

 tion. In view of the fact that no other worker has reported increase of 

 root growth with radiation, Rivera's conclusions need confirmation 

 before being accepted. 



Goodspeed and Olsen (14) stated that a marked acceleration of 

 growth and development may follow appropriate X-ray treatments and 

 Goodspeed (13) reported that on three occasions pot-grown plants of 

 Nicotiana rustica pumila irradiated just previous to first flowering had 

 shown an immediate and very marked growth acceleration. The studies 

 of these authors, however, were concerned principally with the cytological 

 effects of radiation, hence the authors have not published complete data 

 on growth which support the conclusions drawn. 



Stimulative effects of the rays have been claimed by Jacobson (18) 

 who reported that by irradiation the crop of one variety of potatoes was 

 increased 84 per cent in weight over the control plants, while with 

 another variety the increase was as much as 200 per cent. He stated that 

 each tuber was larger than normal and that there was also an increase in 

 total number of tubers. Johnson (22a) in a series of experiments extend- 

 ing over five growing seasons and involving the growth of 17,000 tubers, 

 found that irradiating the unsprouted tubers of the Colorado wild potato 

 {Solarium Jamesii) with a dose of 1500 r-units caused a slightly greater 

 production than from controls. Using the same dose on sprouted tubers 

 caused an increase of over 40 per cent in the average number of tubers 

 per hill with an even greater increase in the average weight per hill. 

 The individual tubers from the treated plants also weighed more than 

 did those from check plants. The conclusion drawn is that increase of 

 rhizome development in the wild potato, which causes formation of a 

 greater number of tubers, is similar to the increased aerial branching 

 which occurs in some other members of this family when the very young 

 plants are treated with medium doses. Sprague and Lenz (62) in a 

 preliminary experiment find results which indicate that strong doses may 

 reduce the number of tubers formed. Such tubers may attain a greater 

 size so that yields of marketable stock are not lowered. In no case, 

 however, did they find the crop increased. 



ShuU and Mitchell (60) in a recent publication report preliminary 

 experiments with very light doses of filtered X-rays which lead them to 

 conclude that stimulative effects may be consistently obtained if appropri- 

 ate conditions are employed. They believe that harmful effects mask 

 stimulation which occurs when the beam is properly filtered. Very 

 small doses of 30 to 120 r-units were used on seedlings of wheat, corn, 

 oats, and sunflower. The treated individuals of the wheat plants were 

 reported taller, of ranker growth,, and exhibiting a higher degree of tiller- 

 ing. Corn rayed 1 to 5 min. showed a higher percentage of germination 

 than the controls, a greater fresh and dry weight of coleoptile, and 



