The SAP in TREES. 23 



tree thus cut, being kept in the fame upright pofitioa in 

 which it grew, on the two following days it bled a little 

 about mid-day ; b\it on each day it became dry, that is, 

 the fap ceafed to defcend whenever the cold of the evening 

 began to take place. 



EXP. ii. February 10. At four o'clock afternoon, during a keen 

 froil, two branches, each five feet long, were cut off a plane- 

 tree. The under fedlions bled rapidly, and the fap freezing 

 as it ran, in half an hour there was a long icicle hanging at 

 each feclion. The two feparated branches, being kept per- 

 pendicular in the open air for half an hour, appeared only 

 moifl at the place where they were cut, but did not bleed. 

 One of them being brought into a warm room, bled copi- 

 oufly for an hour. The other having been flill kept in the 

 open air, had not feparated a drop during that time ; but, 

 upon being removed into the room, it bled freely like the 

 former. 



COR. 17. From thefe experiments, we are, therefore, flill led to 

 conclude, that the fap does not defcend by cold : That when 

 a tree eeafes to bleed by an increafe of cold, this effe6l is not 

 produced by a fubfiding or defcent of the fap ; but that, by 

 the cold, it feems only to be arrefled and held in a ftate of 

 flagnation. 



THE recidivation or ocillatory motion of the fap, by the cold of the 

 night, though long held by philofophers, appears, therefore, 

 to be an erroneous opinion, which has little or no. foundation 

 in nature. 



COR. 1 8. In the lafl experiment, we have the force of the fap's 

 motion, and the influence of the cold upon that force; 

 weighed, the one againft the other. The freezing cold was 

 not able to prevent the motion of the fap upwards, but was 

 powerful enough to obftruc"l its motion downwards. Here, 

 as it was found in many other cafes, the force of the fap 



afcending 



