4 On the MOT '10 N of 



at a fatisfaclory folution of this intricate queftion. For this 

 purpofe, thofe trees which are faid to bleed are the moft conve- 

 nient ; or thofe which, at a certain feafon of the year, have fuch 

 an exuberance of fap, that it flows freely from them upon a 

 flight incifion. PLINY* mentions twice the bleeding of the 

 mulberry ; but he fpeaks of it as an extraordinary phenomenon, 

 and feems to have been unacquainted with the bleeding of the 

 vine. The trees of this fort are indeed more frequent in the 

 cold than in the warmer climates. Some trees of our own 

 country do not bleed, fuch as the oak, a/h r elm, a/pen, hazel \ 

 and hawthorn. Of thofe that bleed, the birch and the plane are 

 the moft remarkable ; and upon thefe the experiments here re- 

 lated were performed. 



IN the laft age, the following important query was propofed 

 on this fubject by Dr LISTER f : 



" WHETHER or not does the fap begin to move in all the parts 

 " of a tree at a time?" 



FIFTY years afterwards, this queftion, ftill unrefolved, was 

 again refumed by Dr HALES :, who, in arguing againft the cir- 

 culation of the fap, exprefles himfelf thus : 



" IF, fays he, early in the fpring, the oak, and feveral other 

 " trees, were to be examined near the top and bottom, when the 

 " fap firft begins to move, fo as to make the bark eafily run or 

 " peel off, I believe it would be found, that the lower bark 

 " would be firft moiftened ; whereas the bark of the top-branches 

 " ought firft to be moiftened, if the fap defcends by the bark." 



OF late years, M. BONNET, when reafoning in favour of a 

 circulation, and againft this fuppofition of Dr HALES, delivers 

 the following remarks : 



" Is it eafy, fays he, exadlly to fix the time when the fap 

 " begins to rife in trees ? That fluid rifes at firft in very fmall 



" quantity ; 



* Nat. Hift. lib. xvi. cap. 38. Lib. xxiii. cap. 7. 

 f Philof. Tranf. anno 1671, p. 2122. 

 J Vegetable Staticks, vol. i. p. 141. 



