On the Formalion of the Bark of Trees. 37 



other side, taking always in a greater or less degree an incli- 

 nation downwards; and when the cellalar substance re- 

 mained united to the iiark at its upper end only, the vessels 

 descended nearly pcrpendiculaily down it; but they did not 

 readily ascend into it, when it was connected with the bark 

 at its lower extremity only : the result ot" similar experiments, 

 when made on different species of" trees, was, however, 

 subject to some variations. 



Pieces of bark of the walnut-tree, which were two inches 

 broad, and four long, having been detached from contact 

 with the alburnum, except at their upper ends, and covered 

 with a plaister composed of bees- wax and turpentine, in some 

 instances, and with clay only in others, readily generated 

 the cellular substance of a new bark ; and between that and 

 the old detached bark very nearly as much alburnum was 

 deposited as in other parts of the tree, where the bark re- 

 tained its natural position ; which, I think, affords very de- 

 cisive evidence of the descent of the sap thrt)ugh the bark. 

 Similar pieces of bark, under the same mode of treatment, 

 but united to the tree at their lower ends only, did not long 

 remain alive, except at their lower extremities; and there 

 a very little alburnum only was generated. Other pieces of 

 bark of the same dimensions, which were laterally united to 

 the tree, continued alive almost to their extremities ; and a 

 considerable portion of alburnum was generated, particularly 

 near their lower edges; the sap appearing in its passaiie across 

 the bark to have been given a considerable inclination down- 

 wards : probably owing to an arrangement in the organisa- 

 tion of the bark, that I have noticed in a former memoir*, 

 which renders it better calculated to transmit the sap towards 

 the roots than in any other direction. 



I have in very few instances been able to make the walnut- 

 tree reproduce its bark from the alburnum, thou<>;h under 

 the same management I rarely failed to succeed with the sy^ 

 camorc and ap|)Ie-tree. Pieces of (he bark of the a|)ple-tree 

 will also live, and generate a small poriion of a'burnum, 

 though only attached to the tree at iheir lower txtreuuties ; 

 probably owing to a small part of the true s.ij) being earned 

 * Philusopiilcal Transaclioiib of ir'0-1. 



C 3 upwards 



