Table 5 



The average diameter of the root, expressed in microns 

 (based on the data of Breslavets and Afanas'eva, 1932*) 



that of the controls, and then becomes consider- 

 ably narrower. It was likewise obvious at a 

 glance that plants which had received favorable 

 doses had larger roots than the controls. We 

 also measured 50 roots from each dose by 

 means of an ocularmicrometric ruler and then 

 transposed the results into microns (these 

 measurements were performed by Lipayeva*). 

 Measurements were always made from the same 

 spot on the root, namely, where the root begins 

 to differentiate into the plerome and the periblem 

 (Table 5) (Fig. 3). 



300 > ^ ^ L. 



UNEXPOSED 250 



FIGURE k. Comparative sizes of ears 

 of control and irradiated rye: 

 a -- control, b -- irradiated.. 



750 2000 8000r 



FIGURE 3. Curve representing changes in the 

 diameter of roots depending 

 on the X-ray dosage used. 



By comparing the average diameters of the 

 roots it was possible to obtain the same kind of 

 a curve as in the case of stem lengths. With a 

 dose of 250 r the curve rises sharply; a dose of 

 500 r continues the rise; with 750 r the curve 

 reaches its apex, after which a gradual decline 

 begins; and at 8000 r the average diameter of the 

 rootlet equals the diameter of the control plants. 



During the spring and summer we performed 



phenol ogical observations, which showed, as 

 with the irradiation of sprouts, that there are 

 no particular differences in the onset of the 

 various phases of ear formation, flowering, and 

 ripening between the irradiated plants and the 

 controls. Individual plants, however, ripened 

 from 8 to 10 days earlier than the controls. 

 This is a point that will bear investigation in 

 the future. 



Upon ripening, the ears of some of the 

 irradiated plants were nearly one and a half 

 times as large as the ears of control plants in 

 our experiment, which, in turn, were consider- 

 ably larger than the ears of plants grown under 



18 



