Mr. Knight on the 
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posed, 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 trans- 
mutation taken place. There is not, however, any thing in 
the preceding cases, calculated to prove that the newly gene- 
rated bark was not converted into alburnum ; and the elabo- 
rate experiments of Du hamel 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 ag- 
gregate, will be found nearly conclusive. 
Examining almost every day, during the spring and sum- 
mer, the progressive formation of alburnum in the young 
shoots of an oak coppice, which had been felled two years 
preceding, I was wholly unable to discover any thing like the 
transmutation of bark into alburnum. The commencement of 
the alburnous layers in the oak ( quercus robur ) 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 itself; and, therefore, if the 
matter which gave existence to the alburnum previously com- 
posed the bark, it must have been, during its change of cha- 
racter, nearly in a state of solution ; but it is the transmutation 
of one organized substance into the other, and not the identity 
only of the matter of both, for which the disciples of Mal- 
pighi contend; and if the fibres and vessels of the bark really 
became those of the alburnum, a very great degree of simi- 
larity ought to be found in the organization of those sub- 
stances. No such similarity, however, exists ; and not any 
