172 



EXPOSED WATER AND FRESHLY FALLEN RAIN 



beaker were inserted the radicles of four germinated seeds of 

 Lu^inus albus to a uniform distance of 10 mm. from the root tip. 

 The radicles were arranged in a circle, in the center of which was 

 suspended the sealed tube, containing 52 mg. of radium bromide 

 of 10,000 activity. The distance from the tube to the radicles 

 was about 10 mm., and the radium salt was opposite the zone 

 of maximum growth. The experiment was set up at 8 : 35 A. M., 

 June 19. Measurements of the amount of growth in length of the 

 radicles were recorded as follows : 



June 19, 5 : 30 P. M. 



June 20, 8 A. M. 



Control 



1 35 mm. 



2 37 



3 37 



4 ^ 

 Total, 148 mm. 



Average, 37.00 mm. 



June 20, 6 P. M. 



Control 



1 50 mm. 



2 57 



3 51 



4 51 



Total, 209 mm. 

 Average, 52.25 mm, 



The results are shown plotted in figure 41, 



