No. 504] PHYSIOLOGICAL EFFECTS OF RADIUM RATS 777 



experiment was set up immediately after the last collec- 

 tion, using radicles of Lupinus albus, immersed to a 

 measured length of 5 mm. in both the fresh and the stale 

 water. Two parallel experiments, A and B, were run, 



Dai/ of month 



each with a "fresh" and a "stale" culture. At the end 

 of 48 hours the lengths of the radicles averaged, for set 

 A, 23.50 mm. fresh; 27.50 mm. stale: for set B, 22.38 mm. 

 fresh ; 27.00 mm. stale. The curves of growth are shown 

 in Fig. 17. The experiments of which this is a type indi- 

 cate that, as a result of its radioactivity, freshly fallen 

 rain water tends to retard the growth of roots. We have 

 as yet no data on the effect of this factor on the activities 

 of the shoot. 



Profound histological changes follow exposure to the 

 rays. These effects are due chiefly to a disturbance of 

 the normal functioning of the cambium, and are in har- 

 mony with results of experiments on animals, in which it 

 has been shown that embryonic tissue is more sensitive 



