OF THE SAP, AND INSENSIBLE PERSPIRATION. 63 



Upward and downward from a wound, at least 

 proportional)] V to the quantity of stem or 

 branch in either direction to supply it. Some 

 authors have asserted that in the heat of tho 

 day it flows most from the lower part of a 

 wound, and in the cool of the eveninp: from 

 the upper ; lience they concluded it was 

 ascending during the first period, and de- 

 scending in the latter. If the fact be true, 

 some other solution must be sought; nor 

 would it be difficult to invent a theory upon 

 this subject : but we rather prefer the investi- 

 gation of truth on more solid foundations. 



Tliis great motion, called the flomng, of 

 the sap, which is to be detected principally in 

 the spring, and slightly in the autumn, is 

 therefore totally distinct from that constant 

 propulsion of it going on in every growinj.'- 

 plant, about which so much has been said in 

 the preceding chapter, and which is proved 

 by taking an entire herb of any kind that has 

 been gathered and suffered to l^egin lo fade, 

 and immersing its root in water. By absorp- 

 tion through the sap-vessels it presently re- 

 vives, for those vessels require a constant sup- 

 ply from the root. 



