EFFECTS ON PLANT RESPIRATION 



20I 



Observations of the amounts of COg given off were recorded as 

 follows : 



Time 



Radium 



Control 



The total amounts of gas evolved during the five days of the 

 experiment were, for the exposed seeds, 7.03 units; for the control, 

 5.57 units. The results for the first nine hours are shown in figure 

 53. There was an apparent initial retardation of respiration during 

 the first hour of exposure, but thereafter the rate was more rapid for 

 the seeds exposed. At the end of the first nine-hour period the radi- 

 ated seeds had evolved a total of 1.83 units of gas, the control seeds 

 a total of 1.20 units. 



The effect on respiration of exposing dry seeds before soaking, and 

 therefore before germination had begun, differs from that of making 

 the exposure only after the seeds were soaked, in that at first there is 

 apparently a retardation of respiration, followed by recovery and ac- 

 celeration, while in the latter case respiration is accelerated from 

 the start. 



