Page:Popular Science Monthly Volume 74.djvu/233

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PSM V74 D233 Thorium radioactive incandescent gas mantle placed above plant seeds.png

Fig. 8.

by the rays from the mantle, and Fig. 9 shows the appearance of the culture seven days after the experiment was started.

The influence of radium rays on photosynthesis was tested in several ways. For example: A nasturtium (Tropœolum) plant was placed in sunlight after having been in darkness for 18 hours. Under one of the leaves, and lightly in contact with it, was placed a Lieber's coated rod of undetermined (probably 25,000) activity. After twenty-four hours the leaf was dechlorophyllized and stained with iodine to test the presence of starch. Starch was almost entirely wanting in the part of the leaf that was directly over the radium-coated rod, but was

PSM V74 D233 Radioactive effects on seedlings close to thorium.png

Fig. 9.