OF BARK INTO ALBUMEN*. 145 



currents when it came into contact with the spaces from which the 

 surface had been scraped off, and to have united again immediately 

 beneath them. 



In each of these experiments, a new cortical and alburnous layer was 

 evidently generated, and apparently by the same means that similar 

 substances were generated beneath a plaister composed of bees-wax and 

 turpentine, in former experiments * ; and the only obvious difference in 

 the result appears to be, that the transposed and newly-generated bark 

 formed a vital union with each other : and it is sufficiently evident, that 

 if bark of any kind was converted into alburnum, it must have been that 

 newly generated. For it can scarcely be supposed, that the bark of a 

 crab-tree was transmuted into the alburnum of an apple-tree, or that the 

 sinuosities of the bark of the crab-tree could have been obliterated, had 

 such transmutation taken place. There is not, however, anything in 

 the preceding cases calculated to prove that the newly-generated bark 

 was not converted into alburnum ; and the elaborate experiments of 

 Duhamel sufficiently evince the difficulty of producing any decisive 

 evidence in this case : nevertheless I trust that I shall be able to adduce 

 such facts as. in the aggregate, will be found nearly conclusive. 



Examining almost every day, during the spring and summer, the pro- 

 gressive formation of alburnum in the young shoots of an oak coppice 

 which had been felled two years preceding, I was wholly unable to discover 

 anything like the transmutation of bark into alburnum. The commence- 

 ment of the alburnous layers in the oak (Quercus robur) is distinguished 

 by a circular row of very large tubes. These tubes are of course gene- 

 rated in the spring ; and during their formation, I found the substance 

 through which they passed to be soft and apparently gelatinous, and much 

 less tenacious and consistent than the substance of the bark itself; and, 

 therefore, if the matter which gave existence to the alburnum previously 

 composed the bark, it must have been, during its change of character, 

 nearly in a state of solution ; but it is the transmutation of one organised 

 substance into the other, and not the identity only of the matter of both, 

 for which the disciples of Malpighi contend ; and if the fibres and vessels 

 of the bark really became those of the alburnum, a very great degree of 

 similarity ought to be found in the organisation of those substances. No 

 such similarity, however, exists ; and not anything at all corresponding 

 with the circular row of large tubes in the alburnum of the oak is dis- 

 coverable in the bark of that tree. These tubes are also generated within 

 the interior surface of the bark, which is well defined ; and during their 



* See the preceding Paper. 



