64 PATTERSON v. M'CAUSLAND.—3 BLAND.

on their first appearance, exhibit only one such leaf or cotyledon,
such as Indian corn, the cabbage tree, (chamaerops palmeto,) &c.;
and hence they have been called monocotyledouous plants. Those
of the first kind having been found to have stems of the exogenous
structure, and those of the latter to be always of an endogenous
formation, the two classes have been and may as well be designated
by the one name as the other. Eaton's Botanical Grammar, 18.

Then assuming that this was the only mode by which exogenous
trees were enlarged, and because the sap flowed more freely and
obviously in summer than in winter, it was affirmed, that the num-
ber of those concentric layers, counting from the surface to the
centre, demonstrated the number of years the tree had been grow-
ing. But as has been seen, it is admitted, that in the wood of for-
est trees of the temperate zone, in which those concentric layers
have been noticed, it has been observed, that each layer is com-
posed of a great number of thinner and scarcely distinguishable
ones, which in some cases assume a more or less conspicuous ap-
pearance than usual, in consequence of the fluctuations of the sea-
sons, or accidental checks on the growth of the tree; as hard win-
ters render the outside, or porus part of each circle, more decided;
while favorable summers make the circle itself altogether broader.

Hence it is evident, from what is thus stated by the advocates
of this notion, of each layer's being an evidence of a year's growth,
that it is founded upon the apparent effects of the revolution of
the seasons in the temperate zone. But the roots of carrots, beets,
&c., which are the growth of a single season; and indeed the roots
of all perennial trees, as well those of the endogenous as of the ex-
ogenous class, are also formed of concentrical layers, Roget Anim.
and Veget. Physi. pt. 1, c. 1, s. 3; and the wood of the trunks of
most of the forest trees of the torrid zone are evidently formed in
the same way; although some of them may exhibit slighter traces
of such concentric rings than others. But the wood of none of the
endogenous class of plants, among which is the cabbage tree (cha-
maerops palmeto,) of * our country, exhibit any such indica-
80 tions of the formation of successive concentrical layers, as
are to be found in a stem of the oak, pine, &c. Rees' Cyclo. v.
Monocotyledon, Palmae, and Wood; Roget. Anim. and Veget. Physi
pt. 1, c. 1, s. 2.

The conspicuous formation of successive layers of wood is, how-
ever, not only confined to trees of a particular class, but even
among them the formation of such layers differs materially, ac-
cording to their respective species, ages, and situation, when

layers, which prolong the existence of the individual."—An Essay on Vege-
table Physiology, by George D. Armstrong, Prof, of Nat. Philosophy and
Chemistry, in Washington College, Virginia, chap. 5 and 6; The Farmers'
Register, by Edmund Ruffin, vol. 7, No. 3.