CIRCULATION OF THE SAP. ©7 



and occasions some degree of growth to take place. But 

 a small portion of that fluid will be carried upwards by- 

 capillary attraction, between the bark and the alburnum, 

 exclusive of the immediate action of the latter substance, 

 and the whole of this will stagnate the lower lip of the 

 wound; where I conceive it generates the small portion 

 of wood and bark, which Hales and Du Hamel have de- 

 scribed. 



I should scarcely have thought an account of the preceding Interesting 



experiments worth sending to you, but that many of the f^^^' respect- 



, . J , , • r • ing the annu- 



conclusions 1 have drawn m my rormer memoirs appear, at lar decortusa-. 



first view, almost incompatible with the facts stated by Hales tionof the fir. 

 and Du Hamel, and that I had one fact to communicate 

 relative to the effects produced by the stagnation of the 

 descending sap of resinous trees, which appeared to lead to 

 important consequences. I have in my possession a piece of 

 a fir-tree, from which a portion of bark, extending round its 

 whole stem, had been taken off several years before the tree 

 was felled ; and of this portion of wood one part grew^ above, 

 and the other below, the decorticated space. Conceiving 

 that, according to the theory I am endeavouring to support. The wood 

 the wood above the decorticated space ought to be much ^^°X^ ^'»^ ^^~ 

 heavier than that below it, owing to the stagnation of the space is muclji 

 descending sap, I ascertained the specific gravity of both '^^i^s'^f' 

 kinds, taking a wedge of each, as nearly of the same form 

 as I could obtain, and I found the difference greatly more 

 than I had anticipated, (he specific gravity of the wood above 

 the decorticated space being 0.590, and of that below only 

 0,491 : and having steeped pieces of each, which weighed a 

 hundred grains, during twelve hours in water, 1 found the lat- 

 ter had absorbed 69 grains, and the former only 51. 



The increased solidity of the wood above the decorticated Whence consi- 

 space, in this instance, must, I conceive have arisen from the ta^l^mz^^h^^' 

 stagnation of the true sap in its descent from the leaves ; and derived in 

 therefore in felling firs, or other resinous trees, considerable f'^^^"'?' 

 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 areto be felled. 

 For mnch of the resinous matter contained in the root^ of 

 these is probably carried up by the ascending sap io the 



F 2 



