No. 504] PHYSIOLOGICAL EFFECTS OF RADIUM RAYS 111 



a culture solution was substituted for the tap-water, the 

 angle of curvature was more abrupt (nearly 90°). It 

 seems probable that this is an indirect response, due to 

 the effect of the radium rays on the water or solution. 



Whether the rays increase the number of ions of an 

 electrolyte in solution is still a debated question, 11 but the 

 physiological effects of tap-water exposed to the rays 

 seem to leave no doubt but that the latter alter a solution 

 in some way. How, we do not know. 



Micheels and de Heen 12 were among the first to study 

 the effect of the rays on plant respiration. Under the 

 conditions of their experiments respiration was always 

 retarded. In one of my own experiments, soaked grains 

 of wheat (Triticum) weighing, when dry, 2 gm., were sup- 

 ported on a moist blotter in a tumbler over a saturated 

 solution of KOH. Over the wheat, and in contact with 

 the grains, was placed the sealed glass tube of radium of 

 1,500,000 activity. The C0 2 given off by the wheat was 

 absorbed by the KOH, and the consequent rise of mercury 

 in a graduated tube of small bore was taken as an index 



11 Cf. Mem. N. Y. Bot. Garden, 4: Chapt. XIX. 1908. 

 "Bull. Acad. Boy. de Belgique Class. Sci., p. 29. 1905. Bot. Cent., 98: 

 646. 1905. 



