EFFECTS ON THE SYNTHESIS OF CARBOHYDRATES I9I 



5, 10, 15 and 30 minutes to the rays from radium of activity 1,800,000 

 and 1,500,000, and from a radium-coated rod (activity undetermined). 

 In order to give a more thorough test for photosynthetic activity, 

 the experiments just described were repeated with the glass tubes 

 containing RaBrg of activities 1,800,000 and 1,500,000 respectively. 

 Exposures were made of 2, 5, 10 and 15 minutes, and the leaves 

 were then tested for both starch and sugar (Fehling's test). Neither 

 starch nor sugar was found in any of the exposed or control leaves. 



2. Effect on the Conversion of Cane-Sugar to 

 Starch in the Dark 



Experiment 71 



In order to test the effect of the rays of radium on the formation 

 of starch by amyloplastids in the dark, two leaves of pumpkin 

 [Peppo)^ taken from a healthy plant kept in the dark for 36 hours, 

 were floated in separate glass dishes on the surface of a 10 per cent, 

 solution of cane sugar, the petioles extending into the solution. 

 Over one leaf (^) was placed a glass tube containing RaBrg 

 (10,000 x). The other leaf served as the control. 



Tests for starch in both leaves at the end of three days showed 

 no effects that could be attributed to the radium. Starch was formed 

 irregularly in both leaves, and similar results were obtained in two 

 repetitions of this experiment, using pumpkin leaves in each case. 



The experiment was repeated with leaves of nasturtium as 

 follows : 



Leaves from a nasturtium plant that had been in the dark-room 

 for 12 hours and found devoid of starch when tested, were floated 

 on the surface of a 10 per cent, solution of cane sugar, in separate 

 glass dishes. Over one of the leaves was suspended the sealed glass 

 tube containing 10 mg. of RaBr2 of 1,800,000 activity, about 3 or 4 

 mm. from the surface of the leaf. 



After an exposure to the radium rays, as described, for 7^ hours, 

 no starch was found in either of the leaves, exposed or control. 

 After an exposure of 29 hours the control leaves were found to have 

 made starch, but no trace of starch could be detected in the leaf 

 exposed to the rays of radium. 



In another repetition of the same experiment, after 20 hours' 

 exposure (as above described) to the rays from RaBrg (1,800,000 x ), 



