136 ON THE ACTION OF THE ALBURNOUS VESSELS. 



true sap in its descent from the leaves ; and therefore in felling firs, or 

 other resinous trees, considerable advantages may be expected from 

 stripping off a portion of their bark all round their trunks, close to the 

 surface of the ground, about the end of May, or beginning of June, in 

 the summer preceding the autumn in which they are to be felled. For 

 much of the resinous matter contained in the roots of these is probably 

 carried up by the ascending sap in the spring, and the return of a large 

 portion of this matter to the roots would probably be prevented * ; the 

 timber, I have however very little doubt, would be much improved by 

 standing a second year, and being then felled in the autumn ; but some 

 loss would be sustained owing to the slow growth of the trees in the 

 second summer. The alburnum of other trees might probably be rendered 

 more solid and durable by the same process ; but the descending sap of 

 these, being of a more fluid consistence than that of the resinous tribe, 

 would escape through the decorticated space into the roots in much 

 larger quantity. 



It may be suspected that the increased solidity of the wood in the fir- 

 tree I have described was confined to the part adjacent to the decorti- 

 cated space ; but it has been long known to gardeners, that taking off a 

 portion of bark round the branch of a fruit-tree occasions the production 

 of much blossom on every part of the branch in the succeeding season. 

 The blossom in this case probably owes its existence to a stagnation of 

 the true sap extending to the extremities of the branch above the decor- 

 ticated space ; and it may therefore be expected that the alburnous 

 matter of the trunk and branches of a resinous tree will be rendered 

 more solid by a similar operation. 



IX. ON THE FORMATION OF THE BARK OF TREES. 



[Read before the ROYAL SOCIETY, February 19, 1807.] 



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 



* The roots of trees, though of much less diameter than their trunks and branches, probably 

 contain much more alburnum and bark, because they are wholly without heart wood, and ex- 

 tend to a much greater length than the branches ; and thence it may be suspected that when 

 fir-trees are felled, their roots contain at least as much resinous matter, in a fluid moveable 

 state, as their trunks and branches ; though not so much as is contained, in a concrete state, in 

 the heart wood of those. 



