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XXIII. On the Inconvertibility of Bark into Alburnum. By 

 Thomas Andrew Knight, Esq'.^F.JR.S. In a Letter 

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



MY DEAR SIR, 



In a letter whicb I had the honour to address to you in the 

 Cnd of the last yearf, I endeavoured to prove that the mat- 

 ter 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 o£ 

 changing into a pulpous and cellular, and ultimately a vas- 

 cular substance ; ihe direction taken by the vessels being 

 apparently dependent on the course which the descending 

 fluid sap is made to take^. The object of the present me- 

 moir is to prove, that the bark thus formed, always remains 

 in the state of bark, and that no part of it is ever trans- 

 muted into alburnum, as many very eminent naturalists have 

 believed. 



Having procured, by grafting, several trees of a variety of 

 the apple and crab tree, the woods of which were distin- 

 guishable from each other by their colours, I took off, early 

 in the spring, portions of bark of equal length, from branches 

 of equal size, and I transposed these pieces of bark, in- 

 closing a part of the stem of the apple tree with a covering 

 of the bark of the crab tree, which extended quite round it, 

 and applying the bark of the apple tree to the stem of the 

 crab tree in ihe same manner. Bandages were then applied 

 to keep the transposed bark and the alburnum in contact 

 with each other ; and the air was excluded by a plaster com- 

 posed of bees- wax and turpentine, and with a covering of 

 tempered clay. 



* From Philosophical Transactions, 1808. 



+ Philosophical Transactions, 1807. 



| I haJ observed tin's circumstance in many successive seasons ; but I was 

 not by any means prepared to believe that such an arrangement could take 

 place in the coagulum afforded by an extravasated fluid ; and I am indebted 

 to Mr. Carlisle for having pointed out to me many circumstances in the mo- 

 tion 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 

 1 have also subsequently to acknowledge many obligations. 



The 



