24:6 FORMATION OF THE BARK OF TREES. 



fore made two circular incisions through the bark, rount£ 

 the stems of several annual shoots of the vine, as early in tho 

 summer as the alburnum within them had acquired sufficient 

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

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

 face of the alburnum 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 generated a cellular sub- 

 stance (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 cellular sub- 

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

 united, and a perfect vascular bark was subsequently formed 

 beneath the alburnum, and appeared perfectly to execute the 

 office of that which had been taken off; the medulla ap- 

 peared to be wholly inactive. 

 Cortical vessels I nave already observed, that the vessels, which were 

 from regenera- generated in the cellular substance on the surface of the al- 

 ia various di- hurnum of the sycamore and the apple-tree, traversed that 

 sections. substance in almost every direction; and the same thing ap- 



pears to occur beneath the old bark, when united to the al- 

 burnum. For having attentively examined, through every 

 part of the spring and summer, the formation of the interna} 

 bark, and al burnous layer beneath it, round the bases of re- 

 generated buds, which I had made to spring from smooth 

 spaces on the roots and stems of trees, I found every appear- 

 ance perfectly consistent with the preceding observations. 

 A single shoot only was suffered to spring from each root and 

 stem, and from the base of this, in every instance, the cortical 

 vessels dispersed themselves in different directions. Some de- 

 scended perpendicularly downwards, whilst others diverged 

 on each side, round the alburnum,' with more or less inclina- 

 tion downwards, and met on the opposite side of it. The 

 same, pulpous and cellular substance appeared to cover the 

 surfaces of the bark and alburnum, when in contact with 



cacb 



