FORMATION OF THE BAUK OF TREES. 24J 



of.tlicm, in the preceding cases, the sup, and consequently 

 the new bark, proceeded; but I was ultimately successful. 



The cellular substance, both in the alburnum and bark of Experiments 

 ,, , . <■ • , • c ,. . on pollard 



old pollard oaks, often exists in masses ot near a Jine in 03 ^ s% 



width, and this organization was peculiarly favourable to my 

 purpose. I therefore repeated on the trunks of trees of 

 this kind experiments similar to those above mentioned, 

 which were made on the walnut-tree. 



Apparently owing to the small quantity of sap, which the 

 old pollard trees contained, their bark way very imperfectly 

 reproduced j but I observed a fluid 10 ouze from the cellular 

 substance, both of the bark and alburnum ; and on the sur- 

 face of these substances alone, in many instances, the new 

 bark was reproduced in small detached pieces. 



I have endeavoured to prove in former communications*, Absorbed fluid 



. . - ^ .' ' , ill- converted into 



that the true sap ot trees acquires those properties which dis- sap by circu ] a . 



tinguish it from the fluid recently absorbed, by circulating tion in the leaf, 

 through the leaf; and that it descends down the bark, where SC e 1M ] s down 

 part of it is employed iri generating the new substances an- the bark, to 

 jmally added to the tree; and that the remainder, not thus ^^ C q^ W SU 

 expended, passes into the alburnum, and there joins the as- 

 cending current of sap. The cellular substance, both of 

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

 experiments, to be capable of affording 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 appear to be capable of an inverted action in giving 

 motion to the fluids which they carry. 



As the power of generating a new bark appeared in the Sap ascending 

 preceding cases to exist alike in the sap of the bark and of shoots can _ e . 

 the alburnum, I was anxious to discover how far the fluid, " e rate new 

 which ascends through the central vessels of the succulent 

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



* Phil. Trans 1801, 1805, and 1806. 



fore 



