CHAPTER IX. 



OF THE SAP, AND INSENSIBLE PERSPl 

 RATION. 



1 he sap of trees, as has been' mentioned in 

 the last chapter, may be obtained by wound* 

 ing a stem or branch in spring, just before 

 the buds open, or in the end of autumn, 

 though less copiously, after a slight frost ; 

 yet not during the frost. In the Palm-trees 

 of hot countries, it is said to flow from a 

 wound at any time of the year. It has al- 

 ways 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, Betula 

 alba, affords plenty of sap; some other trees 

 yield but a small quantity. It flows equally 



