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XLV. Concerning the State in which the true Sap of 

 Trees is deposited during IVinter, In a Letter from 

 Thomas Andrew Knight, Esq. to the Right Hon. 

 Sir Joseph Banks, Bart. K. B. P. R. S.* 



MY DEAR SIR, 



Jlt is well known that the fluid, generally called the sap, in 

 trees, ascends in the spring and summer from their roots, 

 and that in the autumn and winter it is not, in any consi- 

 derahle quantity, found in them ; and I have observed in a 

 former paper, that this fluid rises wholly through the al- 

 burnum, or sap-wood. But Du Hamel and subsequent 

 naturalists have proved, that trees contain another kind of 

 sap, which they have called the true or peculiar juice, or 

 sap, of the plant. Whence this fluid originates does not 

 appear to have been agreed by naturalists ; but I have of- 

 fered some facts to prove that it is generated by the leaf f ; 

 and that it differs from the common aqueous sap, owing to 

 changes it has undergone in its circulation through that or- 

 gan : and I have contended that from this fluid (which Du 

 Hamel has called the sue propre, and which J will call the 

 true sap,) the whole substance, which is annually added to 

 the tree, is derived. I shall endeavour in the present paper 

 to prove that this fluid, in an inspissated state, or some con- 

 crete matter deposited by it, exists during the winter in the 

 alburnum, and that from this fluid, or substance, dissolved 

 in the ascending aqueous sap, is derived the matter which 

 enters into the composition of the new leaves in the spring, 

 and thus furnishes those organs, which were not wanted 

 during the winter, but which are essential to the further 

 progress of vegetation. 



Ytw persons at all conversant with tiniber are ignorant, 

 that the alburnum, or sap-wood, of trees which are felled in 

 the autumn or winter, is much superior in quality to that 

 of other trees of the same species which are suffered to 

 stand till the spring, or summer: it is at once more firm 

 and tenacious in its texture, and more durable. This su- 

 periority in winter-felled wood has been generally attributed 

 to the absence of the sap at that season ; but the appearance 

 and qualities of the wood seem more justly to warrant the 

 conclusion, that some substance has been added to, instead 

 *)£ taken from it, and many circumstances induced me to 



• From Philosophical TraiLsactioiis of 1S05, part i. 

 •}• See Pkilosopliical Trunuirlions of 1801, pajje SSi*. 



114 suspect 



