192 EFFECTS ON THE SYNTHESIS OF CARBOHYDRATES 



the result obtained in that experiment was confirmed, i. e., starch 

 had been elaborated in the control leaf, but not in the one exposed 

 to the rays of radium. 



The exposed leaf was very slightly etiolated. 



The experiment was twice again repeated, once with an exposure 

 to rays from RaBrg of 1,800,000 activity for 30 hours, and again for 

 20 hours. After the 30-hour exposure an abundance of starch was 

 found in the control leaf, but absolutely none in the one exposed to 

 the radium. The exposed leaf was greatly bleached. 



After the 20-hour exposure the exposed leaf was only slightly 

 bleached, and no trace of starch was found in it, while there was an 

 abundance in the control. 



Experiment 72 



To test the effect of exposing the leaf to the radium before feed- 

 ing it with the sugar solution, the following experiment was tried : 



Over a nasturtium leaf still attached to a plant that had been in 

 total darkness for 30 hours, was placed the sealed glass tube of 

 RaBrg (10 mg., 1,500,000 x), just touching the leaf. The plant 

 was left in the dark, and after 29 hours' exposure to the radium, the 

 leaf was cut off and floated on a 10 per cent, solution of cane sugar, 

 in the dark, with two control leaves. 



After 51 hours the three leaves were dechlorophyllized and 

 treated with iodine. No trace of starch was indicated in the leaf 

 that had been exposed to the radium, but an abundance of it was 

 indicated in the control leaves. 



The above experiments show that the rays from RaBr2 of 

 1,800,000 and 1,500,000 activity inhibit the activity of plastids in 

 converting cane sugar to starch. 



Experiment 73 



Two green nasturtium leaves, devoid of starch, were floated on a 

 10 per cent, solution of cane sugar in which the sealed glass tube of 

 10 mg. of RaBrg, of 1,800,000 activity has been immersed for 15 

 hours, and then the tube of 10 mg. RaBrg, of 1,500,000 activity for 

 12 hours. This solution had also stood for two days subsequent to 

 its exposure to the radium ra3's, before being employed in this 

 experiment. 



Control with two leaves floated on a solution not exposed to the 

 rays. 



