EFFECTS OF EXPOSING SEEDS 



119 



less not all of the four seeds of any given set were equally exposed, 

 though great care was taken in this regard. The necessity of using 

 such a small number of seeds was doubtless here (as in other experi- 

 ments) a source of error, by emphasizing individual variations, but 

 this could not well be eliminated on account of the scarcity of the 

 radium, and the comparatively short period of time that any given 

 preparation was at my disposal. 



.10 



11 



12 

 Dau of month 



13 



Fig. 16. Effect on the Growth of Zea Mays of Various Durations of Exposure of 

 the Grains, before Planting, to Radium Rays. Activity, 1,500,000. 



Interpretation of the results is greatly facilitated by inspection of 

 the curves (figures 10-12). In figure 10 it is clearly shown that, 

 for an exposure of 16 hrs., the effect of the rays from the preparations 

 of 1,500,000 X and 1,800,000 X varied directly as the activity of the 

 radium. The same fact is clearly indicated in figures ii and 12, 

 where the exposures were respectively for 24 and 33 hours. 



The immediate effect of exposure for 16 hrs. to the radium of 

 10,000 X (figure 10) was a greater retardation of growth than that 

 produced by the next more active preparation, but from the third day 



