130 EFFECTS OF EXPOSING SEEDS 



November 16, 9 : 30 A. M. 



November 17, 9 : 30 A. M. 



A B C D 



When the duration of the exposure is the same, then the retarda- 

 tion of growth varies directly with the strength of the radium em- 

 ployed. (See FIGURE 23.) 



The 1,800,000 X curve is made to cross the 1,500,000 x curve 

 during the first time interval by the excessive growth of one seedling 

 (No. 6) of the 1,800,000 X culture. It is very probable that this seed 

 was not as effectively exposed as the others. Likewise the initial 

 difference between the average growth of the 10,000 x culture and 

 the control on November 10 would have been greater but for the 

 exceptional growth of seed No. 3, which was either not well exposed 

 to the rays, or else was unusually resistant to their influence. 



In experiments 26, 27, and 28, it was necessary that a longer time 

 should intervene between exposure and planting in some cultures 

 than in others. The following experiment was made in order to see 

 if this variation in time-interval had any effect on the result of 

 exposure for the same length of time to radium of the same activity, 

 at least within the limits imposed in the preceding experiments. 



