SECT. II. ASCENT OF THE SAP. 105 



son of the plant's bleeding, as may be proved by the 

 following experiment : If the bore or incision that 

 has been made in the trunk is minutely inspected 

 while the plant yet bleeds, the sap will be found to 

 issue almost wholly from the inferior side. If 

 several bores are made in the same trunk one above 

 another, the sap will begin to flow first from the 

 lower bore, and ;then from those above it. If a 

 branch of a Vine be lopped, the sap will issue copi- 

 ously from the section terminating the part that 

 remains yet attached to the plant ; but not from the 

 section terminating the part that has been lopped 

 off. This proves indubitably that the direction of 

 tbe sap's motion, during the season of the plant's 

 bleeding, is that of ascent. 



But if the sap flows so copiously during the sea-Itsvelo- 

 son of bleeding, it follows that it must ascend with ciy * 

 a very considerable force ; which force has accord- 

 ingly been made the subject of calculation. To the 

 stem of a Vine cut off about two feet and a half 

 from the ground, Hales fixed a mercurial gauge 

 which he luted with mastic ; the gauge was in the 

 form of a syphon, so contrived that the mercury 

 might be made to rise in proportion to the pressure 

 of the ascending sap. The mercury rose accord- 

 ingly, and reached, as its maximum, to a height of 

 38 inches.* But this was equivalent to a column 

 of water of the height of 43 feet 34- inches ; demon- 

 strating a force in the motion of the sap that, without 

 *Veg. Stat. Exper. 

 1 



