PATTERSON v. M'CAUSLAND.—3 BLAND. 6T

general use is considered as the most valuable of all the timber
trees of our Union, that it attains it largest size and greatest per-
fection in the cold and comparatively barren soil of those swampy
plains, many of which extend in considerable tracts along the
the borders of the Chesapeake, and on the right and left shores of
the lower Potomac; while on the otherwise fertile soils, west of the
mountains, it is by no means so remarkable for its size. Whence
it may be strongly inferred, that a tree, the texture and density of
wood of all the species being known to be alike, may in one situa-
tion attain a much larger size, and in a transverse section of its
trunk exhibit a greater number of concentric circles than another
of the same age the growth of a different situation.

If it be true that trees are enlarged chiefly or only by the forma-
tion of successive concentrical layers, then it necessarily follows,
that those layers, as the tree enlarges, must become wider as well
as longer each year, so as to embrace the whole of its increased
dimensions; and consequently the quantity of wood formed each
year, supposing the several concentrical layers to be of the same
thickness, must increase annually in a compound ratio. But
although such a rate of increase may well be supposed to be car-
ried on during the early years of its growth, there is every reason
to believe, as was observed of the diminished thickness of the last
fifty outside rings of the before mentioned English oak, in the two
hundred of them which were counted from its centre to its surface,
that the concentrical layers become thinner and less distinguisha-
ble as the tree grows older; and in proportion as its roots find it
difficult to draw an increased supply from the soil in which it
stands. These concentrical layers, as they are successively laid on
not only prevent the previous ones from thickening, or enlarg-
ing in any way, except by rising upward, which it is said they do
not do; but as it is thought the continually increasing pressure,
produced by the laying on of new layers, becomes so great as in
many instances to occasion decay and a hollowness of the tree.
Roget Anim. and Veget. Physi. pi. 1, c. 1, s. 3.(c)

(c) "That the upward growth of the stem takes place altogether in the
green shoot of each year, whilst the older portions of the stem undergo no
change in dimensions, is proved by the following fact, known, I presume to
all. When a name is cut upon the bark of the beech tree, (fagus sylvatica,)
the tree-may continue to grow until it has doubled its original height, but
the name will never be raised further from the ground than the point at
which it was originally cut. This process is the same, both in exogens and
endogens."

" Concerning the growth of the fibro-vascular system, i. e. the vascular tis-
sue and woody fibre, there has been a great diversity of opinion among bo-
tanists. By far the greater part of the observations which have been made
for the purpose of examining into this matter, have been made on exogenous
plants; to these, therefore, our attention must be principally directed. But
yet it should be remarked, we can admit no explanation which does not