. Effects of the rays of radium on plants . Experiment 69 May 28, 5 P. M. Under a healthy green leaf on a nasturtium {Tropaeohim) plant that had been in the dark-room for 7 hours, was placed 10 mg. of RaBr2 (1,800,000 X), in a sealed box, por- tected from the leaf by only a thin mica window. After 19 hours' exposure in the dark-room to the radium rays, the radium was removed and the plant placed in the sunlight. After an exposure of 30 minutes to sunlight, the leaf exposed to the radium rays, and a control leaf were tested for starch, with Fig. 48. Experiment 68. Retard- ation of Photosynthesi

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. Effects of the rays of radium on plants . Experiment 69 May 28, 5 P. M. Under a healthy green leaf on a nasturtium {Tropaeohim) plant that had been in the dark-room for 7 hours, was placed 10 mg. of RaBr2 (1,800,000 X), in a sealed box, por- tected from the leaf by only a thin mica window. After 19 hours' exposure in the dark-room to the radium rays, the radium was removed and the plant placed in the sunlight. After an exposure of 30 minutes to sunlight, the leaf exposed to the radium rays, and a control leaf were tested for starch, with Fig. 48. Experiment 68. Retard- ation of Photosynthesis by Radium Rays. The print was made by placing the leaf itself in contact with velox paper in sunlight. Thus the darker portions of the print indicate the more translucent portions of the leaf-blade, due to absence of starch. The darker region was directly over the radium- coated rod.

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