CHANGES ACCOMPANYING BREAKING OF REST PERIOD 13 



After all units were set up in a similar manner, they were con- 

 nected to the same sensitive system. The air was drawn thru each 

 chamber at an avergae rate of three liters per hour, the flow being 

 regulated by means of the thumb screw at "15" (Fig. 2). Each day 

 the air contained in every unit was renewed eight times, which was 

 proven by experiment to be sufficient to obtain all the CO 2 produced 

 by the twigs during twenty-four hours. Suction was provided by 

 a large aspirator bottle. This bottle had a capacity of forty-five 

 liters. Just before the air entered the water bottle, it passed through 

 a CaCU tower. The CaCl 2 retained all moisture which came from 

 the bottle, and which, if not removed, would be taken up by the 

 CaCl 2 tubes attached to the absorption bulbs, thereby increasing 

 their weight unduly. 



The entire apparatus, excepting the aspirator, was placed in a 

 large double-walled box made of heavy galvanized iron (Fig. 1). 

 The space between the two walls (5 cm.) was filled with water which 

 was flowing in and out continually. The doors were also double- 

 walled but they contained no water. The edges of the doors were 

 lined with cotton so they would fit tightly and thereby prevent ex- 

 change of air of different temperatures. The box was placed in a 

 cool north basement room. 



A self-recording thermograph within the box showed an almost 

 horizontal line from day to day. The thermometer registered be- 

 tween 15 and 18 C. 



EXPERIMENT 1. CO 2 PRODUCTION OF TWIGS AS INFLU- 

 ENCED BY PREVIOUS DRYING AND BY FREEZING 



On February 14, 1914, twigs from three King David apple trees 

 were collected and divided in the manner described above. Two 

 lots were placed in a freezing apparatus as shown in the diagram, 

 Fig. 3. The temperature was kept at -15 to -19 C. Two lots were 

 placed in a humidor at room temperature, 18 to 21 C. (See dia- 

 gram, Fig. 3.) Two lots were placed on top of a bookcase where the 

 room temperature varied between 26 and 31 C. In all cases the 

 preliminary treatment lasted sixty hours. Before placing in the 

 respiration chamber, the dried twigs were allowed to regain tur- 

 gidity by immersing them in water for several hours. During that 

 time they imbibed enough moisture to bring them up to within 5 

 per cent of their original weight. 



The data of this experiment are summarized in Tables 1 and 2. 

 The dates show when the material was collected. Calculations of 

 CO 2 productio'n are based on the weights of the twigs just before 



