Supplement to the fourth, fifth and sixth editions of the Encyclopaedia Britannica > Volume 1

306
Common 111. Grew speaks of the existence of vessels in the
Textures, pith of certain plants, as in that of the Fig and the
Pine ; but he adds, that they are usually so postured-
Vpsork in as to form a ring about its margin. [Anatomy of
the Pith. Plants, p. 119.) They are doubtless to be consider¬
ed as enlarged proper vessels, which made a part ox
the first ligneous circle, and have retained therefore
nearly the" situation in which they were originally
formed. Hence, as he observes, they are of divers
kinds, answerable to those of the bark, containing,
in the Fig, a milky juice, and in the Pine, a resinous
substance. Similar vessels, containing a proper juice,
were observed also in the pith of Elder by Malpighi,
who seems to regard such appearances as common,
where the contained juice concretes, or possesses a
dark colour. [Anat. Plantar, p. 4.) It is probable,
however, that the organs here considered to be ves¬
sels, may, in some cases, be cells, into which these
juices have been poured; but where real vessels ot
this kind are found, they are not to be considered as
a part of the original structure of the pith ; but oc¬
curring only in consequence of the changes, which
the vegetable body undergoes in the progress of its
growth.
Its Nature. 112. The general nature of the pith is thus clearly
announced by Grew. “ Although, says he, it
have a different name from the parenchyma in the
bark and the insertions in the wood, yet, as to its
substance, it is the very same with them both ;
whereof there is a double evidence, viz. their conti¬
nuity, and the sameness of their texture ; ’ so that
all these parts are “ one entire piece of work, being
only filled up, in divers manners, with the vessels.
[Anat. of Plants, p. 119-) This continuity of the
pith with the cellular tissue of the bark, by means of
the insertions or transverse ranges of utriculi, as he
calls them, is also adduced by Malpighi as evidence
of the similarity of their nature, and of the pith being,
as it were, an intercepted portion.of the bark {Anat.
Plantar, p. 4—30.); an opinion which seems abun¬
dantly confirmed by the intermixture of the medul¬
lary and cortical textures in many plants, in which,
as already remarked, the distinctive characters of
bark, and pith are alike lost, and the entire stem
exhibits only one uniform appearance of struc¬
ture.
Errors con- 113. The term medulla, employed by the ancients
Cernipg it. Jenotg this texture, derived its origin, no doubt,
from the resemblance which the pith, in the centre
of trees, bore to the marrow in the bones of animals ;
and as the same term, in Animal anatomy, was in¬
correctly employed to express alike the marrow in
the bones, and the nervous substance in the vertebral
column, so the same latitude of signification has been
extended to the vegetable system. Hence, as Mal¬
pighi remarks, the medulla in vegetables was regard¬
ed as analogous, in its nature, to the brain of ani¬
mals, a doctrine which even later writers have con¬
tinued to espouse. It is not our present intention to
describe the uses of the pith, but only to remove, er¬
roneous opinions concerning its nature, and restore
to it that just anatomical character, long since as¬
signed it by Malpighi and Grew; and which some
writers have of late put forth as a considerable no¬
velty.
ANATOMY, VEGETABLE.
Section II. Common
Textures.
Of the Wood or Ligneous Texture. '-'“v-w
114. Immediately surrounding and enveloping the The Wood-
pith, is the part called the wood {lignum vel lignea
portio of Malpighi.) It is essentially composed of
vessels and of cellular tissue, but combined in such
an infinite variety of proportions, and exhibiting such
a boundless diversity of forms, that it is difficult to
seize even its more general features, without the
risk of extending our descriptions beyond the limits
which our plan necessarily prescribes.
115. Except in those vegetables in which no yes- Descrip.
sels have been hitherto demonstrated, but in which tiou.
they must nevertheless be presumed to exist, this
texture may be considered to form a part not only of
every plant, but of all its organs; for into whatever
part fluids are conveyed, vessels must be supposed to
extend; and wherever vessels are present, cellular
tissue is to be found : hence, in its distribution, it
may be considered the most universal of all the tex¬
tures. In trees, the vessels, as we have frequently In ordiuary
remarked, are very numerous, and, when viewed in xre€8.
a transverse section, are seen to be disposed in lay¬
ers or concentric circies around the axis, and to
stand also in lines or radii, diverging from the centre
of the tree. See fig. 4. Flate XVII. Between each
line or ray of vessels, a thin partition of cellular tis¬
sue is interposed, which extends in the dhection of
the ray, through the entire substance of the v\ ood.
At certain distances, varying in different trees, thick¬
er transverse portions of the same substance aie
placed, and are readily distinguishable in almost every
species of wood. Between each layer that is annual¬
ly added to the wood, and each of the smaller lajeis
that go to the formation, of the larger one, cellular
tissue seems also in some trees to be longitudinally
interposed ; so that it is probable, that, in both direc¬
tions, each fasciculus of vessels is intercepted by cel¬
lular tissue, and that in such trees no two fasciculi
are on any side in immediate contact with each other.
It is even probable, that the individual vessels which
contribute to form the fasciculi, are themselves con¬
nected by intervening cellular tissue, which acts like
the neurilema that holds together the filaments of
the fasciculi in the nerves, or the cellular substance
that connects the primary filaments in the muscular
fibres of animals. In this manner, the whole vascu¬
lar system of the plant is everywhere connected and
held together by cellular tissue. Of this tissue, and
the different figures its cells acquire, from the dif¬
ferent modes and degrees, of. compression to which
they are exposed, we have already spoken.
116. In many trees, however, as Palms, the vas-Ia palmS
cular fasciculi, though numerous, are much less a-
bundant than in the examples just referred to. Ihey
are consequently placed at a greater distance from
each otlier, and, not being disposed in regular lines,
do not constitute that radiant appearance so com¬
mon in ordinary trees, but are promiscuously dis¬
persed through the cellular tissue, bee fig. 28.1 late
XVI. As this tissue itself, is not, from the same
causes, compressed either in the direction 01 to the
extent before described, the smaller membranous
partitions that divide the vascular radii from each