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VI. Ow the Inconvertibility of Bark into Alburnum. By Thomas 
Andrew Knight, Esq. F. R. S. In a Letter to Sir Joseph 
Banks, K. B. P.R.S. 
Read February 4, 1808. 
MY DEAR SIR, 
In a letter which I had the honour to address to you in the 
end of the last year,* I endeavoured to prove that the matter 
which composes the bark of trees, previously exists in the 
cells both of their bark and alburnum, in a fluid state, and 
that this fluid, even when extravasated, is capable of changing 
into a pulpous and cellular, and ultimately a vascular sub- 
stance ; the direction taken by the vessels being apparently 
dependent on the course which the descending fluid sap is 
made to take.'f* The object of the present Memoir is to prove, 
that the bark thus formed, always remains in the state of 
bark, and that no part of it is ever transmuted into alburnum, 
as many very eminent naturalists have believed. 
Having procured, by grafting, several trees of a variety of 
* Phil. Trans. 1807. 
f I had observed this circumstance in many successive seasons ; but I was not by 
any means prepared to believe that such an arrangement could take place in the co- 
agulum afforded by an extravasated fluid ; and I am indebted to Mr. Carlisle for 
having pointed out to me many circumstances in the motion and powers of the blood 
of animals, which induced me to give credit to the accuracy of my observations ; and 
to that Gentleman and to Mr. Home, I have also subsequently to acknowledge many 
obligations. 
