of the heart wood of trees. 141 
the spring. But he conceived it to be merely the fluid, which 
was ascending from the earth, at that period ; and he con- 
cluded from subsequent observation and experiment, in the 
same season of the year, and in the summer, that the sap of 
trees chiefly passes up in the vicinity of their medulla, 
through their heart wood. 
M. Coulomb’s statements are, I entertain no doubt, per- 
fectly correct ; but the inferences which he, and other conti- 
nental naturalists have drawn from the facts which he has 
stated, are, I suspect, erroneous. For I have stated in a 
former communication, that when I intersected the alburnum 
of an oak tree in winter, no symptoms of life appeared above 
such intersection in the ensuing spring. A similar experi- 
ment being repeated in the end of June, appeared instantly to 
intercept the whole of the ascending current, and the leaves 
of a tree, of which the heart wood remained entire, faded 
more rapidly than those of another tree of the same species, 
which was felled at the same period, and lay upon the 
ground. In the spring of 1816 also, upon the 1st of March, 
the season of M. Coulomb’s experiments, 1 intersected the 
alburnum of a poplar tree, 1000 parts of which I have stated 
to have contained 684 parts water, and an equal quantity of 
its alburnum 557 parts : yet this tree, notwithstanding the 
immense quantity of water (probably little less than a ton) 
which it contained, exhibited very feeble signs of life in the 
following month, though the weather continued excessively 
wet ; and before Midsummer it was perfectly lifeless. The 
elongated cellular, or (as it is usually called) the fibrous 
texture of the alburnum, through which the sap is now, I 
