The SAP in 'TREES. 39 



fpring feafon, the wood was replete with fap, while the bark was 

 dry. Befides, when the trunk of a tree, for a certain fpace, is 

 decorticated quite round, the pith, in the decorticated part, lives, 

 and all the parts of the tree above it, fo long as the wood con- 

 tinues green, and conveys fap, which it will do for years. The 

 wood appears to be the great fource of nourifhment to all the 

 parts of the tree. It is probable, that, from this alone, the pith 

 is nourifhed, and that its communication with the bark is not 

 to draw nourimment from it, but to afford fome important aid 

 to the growth of the buds. 



7- 



THE important conjecture of Dr HALES, mentioned in the 

 introduction to this paper, and on which he thought the truth 

 or falfehood of the doctrine of a circulation chiefly depended, 

 has been, in the courfe of thefe experiments, completely ve- 

 rified. 



WE have found, that, in the early fpring, the fap firfl begins 

 to move at the bottom of a tree, and proceeds gradually up- 

 wards through all its parts : That the lower bark is firfl moifl- 

 ened, by a fap afcending from the root, and not by a fap de- 

 fcending from the branches, which was generally fuppofed. 

 And further, that, from the firfl movement of the fap in the 

 fpring, till the time of vernation, no defcending fap whatever 

 can be difcerned in the tree. 



THESE, indeed, are important points againfl the doctrine of 

 a circulation, but I do not think that they completely difprove 

 it. They only prove, that there is no circulating fap in a tree 

 during a certain feafon of the year, that is, from the time the 

 tree begins to bleed till the appearance of the leaves. To de- 

 cide the matter finally, it is neceflary, that the route of the fap 

 mould alfo be traced, by accurate experiments, from the time 

 the leaves firfl appear, till the defoliation of the tree in autumn. 

 What the refult of fuch an enquiry might be, I cannot deter- 

 mine : 



