EFFECTS ON THE SYNTHESIS OF CARBOHYDRATES I95 



It was Boehm,' who, in 1883, first demonstrated the power of 

 chloroplasts to form starch in absolute darkness when supplied with 

 cane sugar from a 10 to 20 per cent, solution. This process, in 

 leaves of nasturtium, was completely inhibited, and the leaves 

 bleached by exposures of from 20 to 30 hours to rays from the glass 

 tube of 1,800,000 activity. When the leaf was exposed for 29 hours 

 (1,500,000 x) before being floated on the starch solution, it made no 

 starch in darkness. 



I then reversed the manner of exposure ; that is, I exposed the 

 sugar solution instead of the leaf to the rays. The sealed glass tube 

 containing 5 mg. of radium bromide of 1,800,000 x was suspended 

 in the solution for 15 hours, and then the tube of 1,500,000 x for 12 

 hours longer, giving a total exposure of 27 hours. It was then nec- 

 essary to wait for two days before placing the leaves in the irradiated 

 solution, but, whatever effect the rays had on the solution, it endured 

 for at least two days, for, while some starch was found after eight 

 hours in leaves floated on this preparation, the amount was very much 

 less than that found in similar leaves floated for the same period of 

 time on a portion of the same solution that had not been exposed to 

 the radium. Undoubtedly the effect would have been much more 

 marked had it been possible to use the solution immediately after it 

 had been exposed, but I have not been able to repeat this experiment. 



Bibliography 



I. Boehm, J. Ueber Starkebildung aus Zucker. Bot. Zeit. 41 : 33, 49. 

 18S3. 



