194 effects on the synthesis of carbohydrates 



Experiment 76 

 Into a weak aqueous solution of the chlorophyll paste was placed 

 the glass tube of RaBrg (10 mg., 1,500,000 x ), but after an exposure 

 of four days the chlorophyll was not bleached, nor could any other 

 effect be observed resulting from the influence of the rays of radium. 

 The solution bleached in sunlight as normally. 



Summary 



Using the starch-iodine reaction as a test for photosynthesis, it 

 was found that when a radium-coated rod of 25,000 x was placed 

 over a health}'^ leaf of Phaseolus vulga?'ts for 10 hours in direct sun- 

 light, and at a distance of only 2 or 3 mm., no starch was formed in 

 the narrow region immediately under the rod, though abundantly in 

 the remainder of the leaf. A rod of 10,000 x similarly placed at the 

 same time over another leaf of the same plant had no apparent effect 

 on starch formation. However, to be more sure that the first effect 

 was not due merely to the shading of the leaf by the rod, the experi- 

 ment was repeated, using a leaf of nasturtium [Tropaeoltun majus)^ 

 and placing the active rod under the leaf, and in contact with the 

 under surface. By this method the effect, after an exposure of 24 

 hours, was not so marked, but there was a decided retardation of 

 starch making. A leaf of a nasturtium plant that had been in the 

 dark for 26 hours, and exposed to radium rays (1,800,000 x) that 

 had passed through only a thin sheet of mica for 19 hours out of the 

 26, was then brought into direct sunlight for 30 minutes. The 

 starch-iodine reaction showed less starch in the exposed leaf than an 

 unexposed one from the same plant, and the effect was greatest 

 directly under the mica window through which the radium rays 

 passed. 



An exposure of 24 hours to the rays from radium bromide of 

 1,800,000 X in a sealed glass tube placed under a leaf was followed 

 by no appreciable effect. 



To see if photosynthesis could be stimulated hy short periods of 

 treatment, starch-free leaves of nasturtium were exposed in direct 

 sunlight over sealed glass tubes of 1,500,000 x and 1,800,000 x, 

 and to a radium-coated rod for periods of 5, 10, 15, and 30 minutes, 

 but no effect, of either acceleration or retardation, could be detected 

 by the starch-iodine reaction. In a repetition of this experiment, tests 

 were made for sugar as well as for starch, but with negative results. 



