156 EFFECTS OF RADIOACTIVE AIR ON GROWTH 



growth of roots in an atmosphere containing the decaying radium 

 emanation is more rapid than normally. 



Experiment 47 



In order to see if the emanation given off from about 10 mg. of 

 RaBrj of 7,000 activity, contained in a glass tube open at one end, 

 would affect germination and growth, timothy seed was sown on the 

 surface of the soil in two pots, and each pot was placed under a bell- 

 jar. One bell-jar contained the open tube of radium bromide 

 throughout the experiment, the other served as a control. The 

 radium tube had been open under the first bell-jar for 48 hrs. before 

 the seeds were introduced. 



Observations were continued for nine days, but with negative 

 results. The seeds germinated and grew in both pots, but no sig- 

 nificant difference was detected between the two cultures. 



Summary 



In harmony with results previously obtained under other condi- 

 tions, it is seen that the effect of exposure to the radioactive ema- 

 nation varies with the conditions of exposure. As in Experiment 32, 

 when a layer of moist soil intervened between the radium and the 

 seeds, the rays produced an acceleration of growth, so here, when 

 unsoaked (and hence less sensitive) timothy seeds were planted 

 beneath the soil surface, and the emanation delivered at a distance 

 of 20 mm. above the soil, growth was accelerated. Under similar 

 conditions of planting, but with the emanation delivered at a distance 

 of only 5 mm. above the soil, growth was retarded. Again when the 

 distance was 50 mm., but the timothy sown on the surface of the soil, 

 retardation resulted. The same effect followed when the distance 

 was increased to 190 mm. over timothy seeds sown on moist blotter. 



If, now, the seeds are sown on the surface of the soil, and the 

 emanation delivered, not continuously, as before, but by means of 

 blasts at irregular intervals of from two to twenty-four hours, germi- 

 nation and growth are increased. The growth in length of radicles 

 of Liifimis albiis was uniformly accelerated in an atmosphere con- 

 taining the emanation (figure 33). This result was repeatedly veri- 

 fied and is additional evidence of the greater sensitiveness of tissues 

 containing chlorophyll. An exposure which proved to be an over 

 stimulus for the chlorophyll-bearing shoot system, causing a retarda- 



