Page:Popular Science Monthly Volume 74.djvu/228

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environment, and plant physiology and the newer physics join hands. Here, as elsewhere, the boundaries between the different "sciences" break down.

Fig. 1 is from a photograph of a few of the preparations employed in the experiments about to be described. The three marked R are sealed glass tubes containing radium bromide. The figures indicate the degree of activity of the preparations in terms of the activity of uranium taken as a unit. Radium bromide of 1,800,000 activity is the purest salt thus far obtained. The lower right-hand tube contains radio-tellurium, which gives off only a rays.

The rod below the tubes is of celluloid, coated on one end with radium bromide of 25,000 activity. The radium coating is overlaid with one of celloidin for purposes of protection.

By means of the rod, not only the three kinds of rays, but the emanation as well, are available. The walls of the sealed glass tubes permit the β and γ rays to pass, but the emanation and the α rays not at all.

Radium coatings, such as those on the rod, were devised by Mr. Hugo Lieber, of New York City, and are a valuable aid in studying the physiological rôle of radium. The experiments of the writer, carried on for over three years at the New York Botanical Garden, were made possible solely through the great liberality of Mr. Lieber, who freely supplied all the standard preparations, several thousand dollars worth in all.

In none of the experiments did the radium itself come in contact with the plant tissues. The results noted were due to the action of the rays alone. When the sealed glass tubes were used, the effect was produced by the β and γ rays, acting together; when the radium coatings were employed, by the combined action of the emanation and the rays, α, β and γ.

To review the results obtained by other investigators is beyond the scope and purpose of the present article. Koernicke, Dixon and Wighman, A. B. Greene, Guilleminot and Abbe, not to mention others, have experimented on the action of radium rays on germination and growth, and, to a slight extent, upon other plant processes. There seems to be general agreement among them that the rays exert a retarding or an inhibiting effect, depending upon the activity of the preparation employed and the duration of exposure to the rays.

Germination is easily retarded or inhibited by exposing seeds while dry, or during imbibition of water. In one experiment ten seeds of "Lincoln" oats, after being soaked in water overnight, were exposed for eighteen hours to rays from the tube of 10,000 activity, by being placed with their embryo-sides in contact with the tube. Germination was retarded by this treatment. After being exposed for about 50 hours longer to the same preparation (67 hrs. 35 min. in all), the