_Age of Trees_ (Vol. iv., p. 401.).--Your correspondent L. inquires
after authentic evidence respecting the age of ancient trees:
"In the 12th vol. of Loudon's _Gardener's Magazine_, p. 588., the
Cowthorpe Oak [standing at the extremity of the village of
Cowthorpe, near Wetherby in Yorkshire], is said to be 'undoubtedly
the largest tree at present known in the kingdom.'
"Professor Burnet says, 'the Cowthorpe Oak is sixteen hundred
years old. We may ask, how is this ascertained? From tradition, or
calculated on botanical data? If the latter, it is possibly far
removed from truth. The method of calculating the age of
dicotyledonous trees, with _hollow trunks_' [and he elsewhere
says, so large is the hollow of the Cowthorpe Oak, that it is
reported to have had upwards of seventy persons at one time
therein assembled], 'is by multiplying the number of rings
comprised in a given portion of the remaining wood, by the
proportion which half the entire diameter of the trunk bears to
the selected portion.... It is evident, however, that this
calculation proceeds on the assumption of two circumstances, whose
probable variations may seriously affect the result.
"'1st. That all the rings are of equal width.
"'2nd. That each ring is of uniform width on both sides of the
tree.
"'It is known that the width of the rings diminishes with the age
of the tree, until, at the latter part of its life, they are of
very inconsiderable width, compared with those near the centre of
the trunk.... Again, it is also known that the width of the rings
differs according to season, being of course wider in those
seasons most favourable to the action of the leaves, and the
general processes of growth; but greatly diminished in seasons
affected by blight, cold, or other causes of injury to the leaves.
It also happens that the rings are often of unequal width on
opposite sides of the trunk.... While, if the tree be so hollow as
to have no portion of its centre remaining ... will expose the
calculation to ... error. In reference, therefore, to the
Cowthorpe Oak, we abandon all scientific pretension.'"
The foregoing is extracted from an account of the Cowthorpe Oak by C.
Empson, Esq., 1842: Ackerman, Strand.