Page:Popular Science Monthly Volume 74.djvu/231

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tion. This air was delivered over pots of growing plants or freshly planted seeds in various ways, one of which is shown in Fig. 5, where the radioactive air passed over the soil-surface from an ordinary dovetail

PSM V74 D231 Plant growth retardation by radioactive air in a bell jar.png

Fig. 5.

gas burner. The opening to the outlet pipe is under the flower pot. A control apparatus was similarly arranged, with the exception of the omission of the radium preparation. In one experiment, after a six days' exposure of timothy grass seed, sown unsoaked and covered with only an extremely thin layer of soil, germination and growth were shown to be retarded and the amount of retardation was greatest nearest the point of delivery of the radioactive air (Fig. 6), But where germinated seeds of the white lupine, with radicles marked 10

PSM V74 D231 Plant on left was closer to the radioactive air source.png

Fig. 6.

mm. back from the root-tip, were exposed for twelve hours in the radioactive atmosphere, growth was greater than that of a like number of roots similarly placed in the control jar. In one experiment, for