$ jVCONVEETfBIlITY OF BARK INTO ALBURNUM. 



«vi<ifnt, that if bark of any kind was converted into albur- 

 num, 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 ob- 

 literated, had such transmutation taken place. There is 

 not, however, any thiu^ 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 cas«; nevertheless I trust, that I shall be 

 able to adduce such facts as, in the aggregate, will be found 

 nearly conclusive. 

 Young shoots Examining almost every day, during the spring and sum- 

 ofoak.. No mer, the progressive formation of alburnum in the young 

 of bark into shoots of an oak coppice, which had been felled two years 

 albuvuum. preceding, I was wholly unable to discover any thing like 

 the transmutation of bark into alburnunj. The commence^ 

 ment of the alburnous layers in the oak fqnercus roburj is 

 distinguished by a circular row of very large tubes. These 

 tubes are of course generated 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 it- 

 self; 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 organized sub- 

 stance into the other, and not the identity only of the mat- 

 ter of both, for which the disciples of Malpighi contend; 

 and if the tihres and vessels of the bark really became those 

 of the alburnum, a very great degree of similarity ought to 

 be found in the organization of tiiose ^5ubstances. No such 

 :*imilarity, however, exists; and imt any thing at all corres- 

 ponding with the circular row of large tubes in the albur- 

 num of the oak is discoverable in the bark of that tree. 

 These tubes are also generated within the interior surface of 

 the bark, which is well dctined ; and during their formation 

 the vessels of the bark are distinctly visible, as different or- 

 gans : and had the one beea transmuted into the other, their 



progressive 



