﻿i9i6] A PPLEMA A* — RES T PERIOD 287 



bells a nearly saturated atmosphere. Equal quantities were added 

 to each pot. Thermometers were placed inside the bell glasses 

 and the temperatures recorded early in the morning and in the 

 afternoon. The temperatures ran practically the same under all 

 the bells, except the clear one, which showed an average of 1-2 0 

 higher than the others (table XX). 



TABLE XX 



The experiment recorded in table XX shows not only the stimu- 

 lating effect of light on the growth processes in the buds, but also 

 suggests that this effect is due to a greater oxygenation of the tissues 

 by photosynthesis. The chief evidence for this conclusion lies in 

 the fact that the tubers under the blue bell glass sprouted very 

 little earlier than those under the black bell glass. Although the 

 tubers under the blue bell glass soon became green, little photo- 

 synthesis would be expected, on account of the slight energy for this 

 process in the actinic rays. Subdued light does not hasten the 

 sprouting of the tubers with well suberized skins; the effect is rather 

 one of slight retardation. The rest period of tubers with heavily 

 suberized skins may be considerably extended by thorough green- 

 ing in full light. 



Effect of hydrogen peroxide. — If the skin is in any degree- 

 permeable to hydrogen peroxide, the abundance of catalase in 

 potato tubers would decompose it, liberating free oxygen. Earlier 

 sprouting would then be expected if oxygen is a limiting factor for 

 growth under normal conditions. Experiments to test this hy- 

 pothesis were conducted as follows: Tubers were wrapped in cot- 

 ton saturated with dioxygen, then stored in moist chambers, which 

 were buried in wet sawdust underneath a greenhouse bench. 



