152 EFFECTS OF RADIOACTIVE AIR ON GROWTH 



shorter than the control plants, but the difference is not so marked 

 as it was 3 days ago, i. e., 4 days after the exposure. 



On June 10 the control seedlings averaged about one fourth taller 

 than those exposed. On June 15 the cultures were photographed 

 (figure 32). 



Retardation of germination and growth has followed exposure as 

 described. 



This experiment was repeated and similar results were obtained. 



Experiment 44 



Object : To ascertain the effect of germinating and growing 

 timothy grass seed in an atmosphere containing the radium emanation. 



Seeds of timothy grass {Phleum -pratcnse) were planted on the 

 surface of the soil in each of two pots, and each pot was placed un- 

 der a bell-jar with a tubulure at the top and bottom. By means of a 

 blast bulb the emanation from RaBrj was forced into the bell-jar at 

 irregular intervals of from 2 to 24 hours from a cylinder lined with a 

 " Lieber's radium-coating." Blasts of ordinary air were similarly 

 forced through the control jar. 



The emanation was delivered at a height of about 90 mm. above 

 the seeds, and the periodic blasts were continued for ten days. 



On the tenth day the exposed plants were slightly but definitely 

 taller, on the average, than the unexposed plants, and on the eleventh 

 day they were still taller than the control. On the twentieth day 

 after planting the same difference in height was maintained and the 

 experiment was discontinued. 



Experiment 45 

 Object : To ascertain the effect of growing germinated seeds of 

 Lu^inus albus in an atmosphere containing the emanation of radium. 



April 29, 12 M. 



On the radicles of five germinated seeds of Lti^inus albus, ger- 

 minated in moist sphagnum until the radicles were over 10 mm. long, 

 were placed reference marks in India ink, 10 mm. from the root-tip. 

 The seedlings were suspended on glass spits under a bell-jar into 

 which the radium emanation was drawn, as described in Experi- 

 ment 44. 



Five germinated seedlings were similarly arranged in a control 

 jar. 



