IV. On the 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, An extraordinary diversity of opinion appears to have pre­vailed among naturalists, respecting the production and sub­sequent state of the bark of trees. According to the theory of Malpighi, the cortical sub­stance, 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.