On the Formation of the ark of Trees. 39 



antiually added to the tree; and that the remainder, not thus 

 expended, passes into the alburnum, and there joins the 

 ascending current of sap. The celluhir substance, both of 

 the bark and alburnum, has been proved, in the preceding 

 experiments, to be capable of afibrding the sap a passage 

 through it; and therefore it appears not very improbable, 

 that it executes an office similar to that of the anastomosing 

 vessels of the animal economy, when the cellular surfaces of 

 the bark and alburnum are in contact with each other ; and, 

 when detached, it may be inferred, that the passing fluid will 

 exude from both surfaces : because almost all the vessels of 

 trees aj*pear to be capable of an inverted action in giving 

 motion to the fluids which they carry. 



As the power of generating a new bark apjieared in the 

 preceding cases to exist alike in the sap of the bark and of 

 the albiarnum, I was anxious to discover how far the fluid, 

 which ascends through the central vessels of the succulent 

 annual shoot, is endued with similar powers. Having there- 

 fore made two circular incisions through the bark, round 

 the stems of several annual shoots of the vine, as earlv in the 

 summer as the alburnum within them had acquired sufficient 

 maturity to perform its office of carrying up the sap, I took 

 off the bark between these incisions ; and I abraded the sur- 

 face of the alhurnum to prevent a reproduction of it. The 

 alburnum in the decorticated spaces soon became externally 

 dry and lifeless ; and several incisions were then made lon- 

 gitudinally through it. The incisions commenced a little 

 above, and extended below the decorticated spaces, so that, 

 if the sap of the central vessels gcncra,ted a cellular substance 

 (as I concluded it would), that substance might come into 

 contact and form a union with the substance of the same 

 kind emitted by the bark above and below. 



The experiment succeeded perfectly, and the ccllulav sub- 

 stances gencrateil by the central vessels, and the bark, soon 

 united, and a perfect vascular bark was subsequently formed 

 bcneatli the alburnum, and apjicared perfectly to execute ihc 

 office of that which had been taken off; the medulla ai;iijeared 

 to be wholly inactive. 



\ have already observed, that the vessels, \\ luch were l''c- 

 C 4 ncraled 



