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CHAPTER IX. 



OF THE SAP, AND tNSENSlBLE PEKSPIUATION-. 



The sap of trees, as has been mentioned in the last 

 chapter, may be obtained by wounding a stem or branch 

 in spring, just before the buds open, or in the end of au- 

 tumn, though less copiously, after a slight frost ; yet 

 not during the frost. In the Palm-trees of hot coun- 

 tries, it is said to flow from a wound at any time of the 

 year. It has always been observed to flow from the 

 young wood or alburnum of our trees, not from the bark ; 

 which agrees with Mr. Knight's theory. 



A common branch of the Vine cut through will yield 

 about a pint of this fluid in the course of twenty-four 

 hours. The Birch, Betida alba, affords plenty of sap ; 

 some other trees yield but a small quantity. It flows 

 equally upward and downward from a wound, at least 

 proportionably to the quantity of stem or branch in eith- 

 er direction to supply it. Some authors have asserted 

 that in the heat of the day it flows most from the lower 

 part of a wound, and in the cool of the evening from the 

 upper ; hence they concluded it was ascendiu": duriiiP- 

 the first period, and descending 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 investigation of truth on more 

 solid foundations. 



This great motion, called the Jlozving, of the sap, 

 which is to be detected princip illy in the spring, and 

 -slightly in the autumn, is theretoie totally disiiact from 



