764 



THE AMEBIC AN NATURALIST [Vol. XLII 



plants. If this stimulus ranges between a minimum and 

 an optimum point an excitation of function results ; if be- 

 yond the optimum point a depression of function, passing 

 to complete inhibition as the strength or duration of the 

 treatment is increased beyond the point of optimum 

 stimulation. The following experiments are chosen 

 from nearly 200, and indicate the nature of the evidence 

 upon which the above conclusions are based. 



Eight dry seeds of the bean (Phaseolus— Henderson's 

 "Long Yellow, Six Weeks") were placed in moist sphag- 

 num with their hilum-edges touching a rod coated with a 

 Lieber's radium-coating 8 of 10,000 activity. 9 After 











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1 1 c 



T > > ^ 



r J f t 



# > % *T 



*f % <? 



three days (70 hours) exposure, the radicles of the ex- 

 posed seeds averaged 13.18 mm. in length, those of a con- 

 trol set 15.12 mm. Ten dry seeds of Lupinus albus were 

 similarly exposed to a coated rod of 25,000 activity and, 



» See Gager, I. c, Chapt. VI. 



