124 EFFECTS OF EXPOSING SEEDS 



November 2, 9 : 30 A. M. 



B 



50 hrs. 

 19.00 mm. 

 12.50 

 20.00 

 19.00 

 0.00 

 21.00 



91.50 mm. 

 18.30 mm. 



November 3, 9 : 30 A. M. 



B 



50 hrs. 



19.00 mm. 

 12.50 

 21.00 

 21.00 

 0.00 

 21.50 



95.00 mm. 

 19.00 mm. 



In the 72-hrs. culture the plumule is above the partly opened 

 cotyledons in only two seedlings. In the other three cultures the 

 plumule is well above the spreading cotyledons. The effect on the 

 root-system is shown in figure 20. 



November 5. 



No apparent growth of the hypocotyl has taken place in any of 

 the cultures since November 3, but the epicotyl has grown in all the 

 plants of all four cultures, except four plants of the 72-hrs. exposure. 



November 14. 



The experiment was photographed (see figures 19 and 20), and 

 portions of the hypocotyls were preserved for sectioning (see p. 224). 



The experiment clearly shows that, when the activity of the radium 

 is the same, retardation of germination and growth varies directly 

 with the duration of the exposure (see figure 21). 



