EFFECTS OF EXPOSING SEEDS IO7 



from 15-35 mm. long. The relative lengths of the radiated and 

 control seed hypocotyls were not recorded. 



Both sets of seeds were placed to develop further in moist 

 sphagnum. 



March 17, 9 : 30 A. M. 



The tap-roots of the radiated plants have failed to develop 

 normally, being not more than one half to one sixth as long as those 

 not exposed to the radium rays. Correlated with the failure of the 

 tap-root to develop, the secondary roots are more fully developed in 

 the radiated seedlings, but there was no difference ii^ growth of sec- 

 ondary roots on the side of the hypocotyl that was next to the radium- 

 tube during exposure and those on the opposite side. 



Experiment 25 

 March 22, 4 P. M. 



Ten soaked seeds of " Lincoln " oats (^Avena), with the glumes 

 removed, were placed in a Zurich germinator, in parallel rows of 5 

 each, in contact with the glass tube of RaBrg (10,000 x ) with the 

 radium evenly distributed over the bottom of the tube. The radicle 

 ends of the oats were all touching the glass tube. 



Control of 5 seeds with empty tube, similarly placed, and both 

 sets placed in the dark room to germinate. 



March 23, 11 A. M. 



All the grains have germinated in both cultures, but those under 

 the radium are only about one half as far developed as the control 

 grains. 



March 26, 11 A. M. 



All the grains have grown since the last observation, but the 

 control grains have grown more than those radiated. Two secondary 

 roots have developed on each control grain, no secondary roots on 

 the radiated grains. The grains of both sets were planted in soil 

 and placed in the propagating house to develop. The total length 

 of exposure to the radium has been 67 hrs. 35 min. 



March 31, 9 : 30 A. M. 



The experiment was photographed. The control plants are 

 several times taller than those from exposed seeds (figure 8). 



