A 



JOURNAL . . 



OP 



NATURAL PHILOSOPHY, CHEMISTRY, 



AND 



THE ARTS. 



APRIL, 1808. 



ARTICLE I. 



On (he formation of the Bark of Trees. In a Letter from T. A, 

 Knight, Esq. F. R. S. to the Right Honourable Sir Joseph 

 Banks, K. B. P. R. S. #c*. 



My Dear Sir, 



.A.N extraordinary diversity of opinion appears to have Vaiious 

 prevailed among naturalists, respecting the production and opinions re- 

 subsequent state of the bark of trees. production ©f 



According to the theory of Malpighi, the cortical sub- bark, 

 stance, which is annually generated, derives its origin from 

 the older bark ; and the interior part of this new substance is 

 annually transmuted into alburnum or sap wood; whilst the 

 exterior part, becoming dry and lifeless, forms the exterior 

 covering or cortex. 



The opinions of Grew do not appear to differ much from 

 those of Malpighi ; but he conceives the interior bark to con- 

 sist of two distinct substances, one of which becomes albur- 



* Philos. Tras. for 1806, Part I, p. 103. Sir Godfrey Copley's gold 

 medal for 1806 was adjudged to Mr. Knight for his various papers on 

 vegetation printed »n the Phil. Trans. 



Vol. XIX. No. 84.— April, 1808. R num. 



