ipO EFFECTS ON THE SYNTHESIS OF CARBOHYDRATES 



iodine. Starch was found in all parts of both leaves, but the iodine 

 gave a much darker stain, and more evenly distributed in the control 

 leaf, while in the radiated leaf the color was decidedly lighter, and 

 lightest in the region that was directly over the radium, growing 

 gradually darker toward the margin of the blade. 



Apparently a slight retardation of starch-synthesis has followed 

 the exposure to the radium rays. 



Experiment 70 



A nasturtium {Tropaeoltim) plant was removed to the light after 

 being in the dark-room for 18 hrs., and under one of the healthy 

 leaves was placed the sealed glass tube of RaBrj (1,800,000 x ), the 

 tube lightly touching the leaf in places. 



After an exposure to the radium of 24 hours the leaf was tested 

 for starch (10 A. M.), but the differences in the staining were not as 

 marked as when the coated rod was used. 



Experiment 70a. 



In order to see if an exposure to radium rays for shorter periods 

 of time would be followed by an acceleration of photosynthesis, the 

 following experiment was tried : 



From a healthy nasturtium plant {Tropaeolum majus) that had 

 been in total darkness for 12 hours three vigorous leaves were de- 

 tached and exposed to the direct rays of the sun as follows : 



No. I lying on a glass tube of RaBr2 of 1,800,000 activity. 



No. 2 lying on a glass tube of RaBrg of 1,500,000 activity. 



No. 3, Control. Not exposed to radium rays. 



The leaves were all destitute of chlorophyll at the beginning of 

 the experiment. Four exposures were made as described, one each 

 of 2, 5, 10 and 15 minutes. 



On decolorizing the leaves and staining with iodine no difference 

 could be detected in the reaction for starch. No starch was indi- 

 cated in any of the leaves. On examination with the microscope, 

 also, no starch was found, except, of course, in the guard cells of 

 the stomata, as would be expected under normal conditions. 



The results were negative. 



A repetition of this experiment with leaves that had been in the 

 dark room for 48 hrs. also gave negative results after exposures of 



