264 



ESMOND R. LONG 



stroyed, while in the day the reverse process takes place, so that 

 the acidity of the sap is higher at the day's beginning than at 

 its close. 



It would be expected furthermore that the accumulation of 

 acidity during the night would bf the greatest where the concen- 

 tration of carbohydrates is greatest, that is in the outer parts 

 near the chlorophyll tissue, the seat of carbohydrate formation, 

 and this is confirmed by the analytical tests. Taking the figures 



TABLE 1 



Shoiving dry weight {in per cent), density of sap, and acidity of sap in three samples 

 at different depths from each of three plants of Carnegiea. All plants collected 

 July 18; analyses made at 5 p.m. on July 18, 19, and 21 , and at 8 a.m. on the morn- 

 ings following. Plant No. 1 : height 126 cm., sampled 70-90 cm. from base; No. 2: 

 height 134 cm., sampled 80-100 cm. from base; No. 3: height 110 cm. sampled 

 55-75 cm. from base 



Large amount of air in sap. 



from table 1 and subtracting the late afternoon value for acidity 

 from that of the early morning, we obtain the results shown in 

 table 2. 



The difference between morning and evening acidity is thus 

 seen to be relatively great in the outer parts and slight in the cen- 

 tral tissues. This is probably to be explained as follows. Near 

 the surface of the plant, where soluble carbohydrates are plenti- 

 ful, we have a relatively large carbohydrate metabolism as com- 

 pared with the inner tissues, which because of their distance 



