fbt SAP in 'TREES. 25 



was the firft inftance of many which afterwards occurred, to 

 ihew, that, in the early fpring, a tree bleeds by heat, and, as 

 the feafon advances, by cold. 



APRIL i. 



Thermometer, at noon, 50. ; at midnight, 34. 

 No obfervation becaufe of rain. 



APRIL 2. 



Thermometer, at noon, 46.; at midnight, 39. 

 THE feventh incifion, being the one immediately under the 

 branches, bled ; but the eighth, and all the other incifions above 

 it, upon the trunk, were dry. The inverted branch D E Hill 

 bled at E, but not in fuch abundance as formerly. 

 OBS. 28. It is remarkable, that the eighth and ninth incifions, 

 which had formerly bled, were dry for fome days paft, though 

 the four branches above them bled freely. It appears, that, 

 when the fap rifes to the juncture of branches, it is there led 

 off rapidly by the younger wood. By this means, the branches 

 become replete with fap ; the adjacent parts of the trunk are 

 drained, and ceafe to bleed ; while the fap, in the younger 

 wood of the branches, flows plentifully. 

 ANOTHER cafe, analogous to this, was found in the following 

 experiment : 



EXP. 12. The grey willow* is a tree which does not bleed ; but 

 when the fap afcends in fpring, it rifes vifibly between the 

 wood and bark, though not fo copioufly as to bleed ; yet 

 wherever it arrives in fufEcient quantity, it makes the bark 

 feparate eafily from the wood, as in the birch, and probably 

 in all other trees. 



ON the igth of April, the bark of this tree was found to fe- 

 parate freely from the wood, where the branch was of four 

 years growth. It feparated ftill more freely where the branch 



D was 



* Salix caprea, LIN. 



