RADIUM RAYS 



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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 dove- 



Fin. 5. 



tail 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 



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 



