64 OF THE SAP, 



This flowing of tlie sap lias been tliouglit 

 to demonstrate a circulation, because, there 

 being no leaves to carry it off by perspiration, 

 it is evident that, if it were at these periods 

 running up the sap-vessels with such velocity, 

 it must run down -again by other channels. 

 As soon as the leaves expand, its motion is 

 no lonsrer to be detected. The effusion of 

 sap from plants, when cut or w^ounded, is, 

 during the greater part of the year, compa- 

 ratively very small. Their secreted fluids run 

 much more abundantly. 



I conceive therefore that xKis flowing is no- 

 thing more than a facility in the sap to run, 

 owing to the peculiar irritability of the ve- 

 getable body at the times above mentioned ; 

 and that it runs only ^hen a wound is made, 

 being naturally at rest till the leaves open, 

 and adniit of its proper and regular convey- 

 ance. Accordingly^ ligatures made at this 

 period, which show so plainly the course of 

 the blood in an animal body, have never 

 been found to throw any light upon the vege- 

 table circulation. This great facility in the 

 sap to run is the first step towards the revi- 

 val of vegetation from the torpor of winter ; 



