LIGHT AND SUBTONICITY 77 



preliminary down-curve, a transitory acceleration of growth. 

 This was followed by the normal retardation as shown b}' 

 the up-curve. On the cessation of light, there was a 

 restoration of the normal rate as seen in the horizontal 

 record at the top of the curve ; but after a while the balance 

 was upset in the opposite direction, exhibiting a rate above 

 the normal. Finally, the rate of growth became restored 



Fig. 38. Response of subtonic specimen to stimulus of light. 



Note preliminary acceleration of growth followed by retardation 

 (up-curve) ; after-effect, an enhanced rate of growth followed 

 by recovery (seedling of Wheat). 



to the norm.al, as seen in the curve becoming once more 

 horizontal (fig. 38). 



The curves given in figs. 37 and 38 are essentially similar. 

 The only difference is in the preliminary acceleration of 

 growth which, as will be shown in the next chapter, is the 

 temporary effect of stimulation on a subtonic tissue. 



A second record was taken with the identical specimen, 

 the intensity of light being increased by bringing the arc- 

 light nearer the plant. In this experiment retardation of 

 growth occurred from the very beginning. This was for 

 two reasons : (i) the increased intensity of light was now 



