AN ENCYCLOPAEDIA 
OF HORTICULTURE. 153 
Vessels—continued. 
bundles there are “spiral” or annular" Vessels. These 
are long, slender tubes, which appear round in transverse 
section. They frequently show very slight traces of the 
cells of which they were built up. 
feature in them is the existence of a peculiar thickening 
deposit in the vessel, which, in a longitudinal section 
of the bundle, is not unlike a glass tube inclosing a 
closely-wound spiral wire, or wire rings; or a more 
familiar comparison may be made with an indiarubber 
tube, kept open by a wire spirally coiled in its interior. 
Besides spiral and annular Vessels, the wood-bundles very 
generally contain others, in which the thickening deposits 
are laid down on the inner surface of the walls in the 
form of a more or less regular network (“ reticulated 
Vessels"), or of the steps of a ladder (“scalariform 
Vessels" of Ferns and their allies), or covering the wall, 
so as to leave only narrow tubes or pits through the 
new layers (“ pitted or dotted Vessels,” or “ Ducts”). All 
these Vessels show an angular form in transverse section ; 
and they are generally wider than the spiral Vessels. 
They also show distinctly the boundaries of the cells of 
which they are built up; though the openings from cell 
to cell are always relatively large. Spiral and annular 
Vessels are very rarely formed by the cambium; hence, 
in Dicotyledons and in Conifers, they are present in the 
stems and roots usually only in the earliest-formed wood 
—41.e., they surround the pith; and, at one period, they 
were supposed to form around the pith a peculiar organ, 
which was called the “medullary sheath." In Dicoty- 
ledons, the Vessels in the wood formed by the cambium 
are almost all reticulated, dotted, or pitted. In Conifers, 
very few Vessels are formed by the cambium, their work 
being done by wood-cells, with openings from one to the 
other of a peculiar nature. All the characteristic Vessels 
of the Wood very soon lose their protoplasm, and contain 
only air or sap, or, more generally, both air and sap. 
The walls of fully-formed Wood-vessels are lignified and ` 
firm x 
The Vessels of the Bast are very distinct from those 
of the wood. .They are always present in the soft bast 
(though not always easily detected, except by an expert 
microscopist); but a few may also be found in some 
plants in the pith or the cortex. They assume the form 
of slender tubes, with thin, flexible walls, unmarked by 
thickening deposits. The walls separating the cells that 
make up these Vessels are not entirely absorbed (as is 
the ease in the Wood-vessels) They can always be 
recognised as cross-partitions; but they are pierced by 
numerous small openings, so as to resemble a sieve, 
whence they are called * sieve-plates," and the Vessels 
are called “sieve-tubes.” Often, the side walls of ad- 
joining tubes also show sieve-plates. The sieve-tubes 
retain their protoplasmic contents; and the protoplasm 
extends through the sieve-plates. Sachs believes that 
the new protoplasm is largely produced in the sieve- 
tubes; and there is no doubt that they are the channels 
by which the protoplasm is chiefly, if not entirely, 
carried from one part of a plant to another, as may be 
required during growth. 
The Vessels of the ground-tissue are of far less general 
occurrence than those of the vascular system; and they ` 
are very different from these in their nature, if we except 
_ the small, scattered bundles of sieve-tubes that traverse the 
ground-tissues of certain plants. The only form of ground- 
tissue Vessels that calls for special mention is that contain- 
ing “latex,” from which the Vessels themselves are called 
“ Laticiferous Vessels.” They exist only in certain orders 
of plants, chiefly among Dicotyledons, e.g., Campanulacee, 
many Composite, Euphorbiacew, Ficoidem, Papaveracee. 
Among Monocotyledons, they can scarcely be said to exist 
in their characteristic form, or with their characteristic 
contents. ^ Latieiferous Vessels vary in their mode of 
origin in different plants. In most (e.g., Poppies, Dande- 
Vol. IV. ` 
The characteristic . 
Vessels—continued. 
lion), they are formed, like other Vessels, by the union of 
cells, of which the dividing-walls are entirely or partially 
absorbed. Thus very irregular Vessels are formed, which 
unite freely with one another by branches, so as to form 
a copious network, with free inter-communication. The 
walls of these Vessels seldom show thickening deposits. 
In a few orders (Asclepiadew, Ewphorbiacee), the Latici- 
ferous Vessels are probably formed, not by the union of 
cells, but by the elongation and branching of cells, which 
are not divided by cross-partitions, and which thus reach 
a very great length. It is believed, by many botanists, 
that the Laticiferous Vessels of some plants (eg. Rhus) 
are really intercellular spaces, into which the latex is 
poured. The Laticiferous Vessels frequently accompany 
the sieve-tubes, and may even take their place to 
some extent. In those Monocotyledons that possess 
latex, it is contained in rows of large cells, separated by | 
walls, in which perforations have not been clearly made 
out (Allium Cepa); or, in those plants (Galanthus) in 
which the Vessels consist of cells, with perforated walls, 
the contents do not resemble latex, but are only clear sap, 
with raphides, i.e., slender crystals of Oxalate of Lime. 
The latex, in Dicotyledons, is a peculiar fluid, which at 
once appears on breaking any part of a plant in which it 
exists. It is clear while in the uninjured tissues; but on 
exposure to the atmosphere, on a broken surface, it becomes 
turbid. It is then white, like milk, in most plants; but 
in some it is coloured yellow (Chelidonium) or orange by 
pigments in it. The microscope shows that it is chiefly 
composed of watery sap, in which float myriads of ex- 
tremely minute granules: these, as in milk, are the cause 
of its opaque, white appearance when exposed to the air. 
On continued exposure to the air, or mixture with alcohol, 
acids, Ze, masses separate from the latex in the form of 
* eoagula," which usually become dark in colour. These 
coagula often afford useful products, e.g., Opium, and 
Caoutchouc, or Indiarubber. They vary considerably in 
composition, texture, and properties. The latex usually 
has dissolved in it small quantities of sugar, gum, proto- 
plasm, and alkaloids; and starch granules are present in 
the latex of some plants (Euphorbia). In the Papaw 
(Carica. Papaya), there is a peculiar substance (“ papa- 
yotin") dissolved in the latex, which exerts a digestive 
action on muscular fibre. It is believed by many botanists 
that the Laticiferous Vessels may be of the same use in 
plants that veins are in animals; but the plants that 
possess them are comparatively few, and there is never 
a central organ for propelling the latex, as the heart 
propels the blood. The latex, like the blood, contains sub- 
stances employed in the nutrition of the plant, and also 
substances that must be regarded as mere excretions 
formed during the processes of growth, and that would be 
hurtful if allowed to remain in the cells. Laticiferous 
Vessels are confined to the higher plants; but Laticiferous 
cells occur among some of the cellular Cryptogams, and 
notably in the genus Lactarius, among Mushrooms, 
VESTIA (named in honour of L. C. de Vest, 1776-1840, 
Professor at Gritz). ORD. Solanacee. A monotypic 
genus. The species is an interesting, erect, glabrous, 
much-branched, greenhouse shrub. For culture, see 
Cestrum. 
V. lycioides (Lycium-like), Chilian Box-thorn. , f. yellow, 
solitary or few at the tips of the branches, pen ; calyx 
shortly five-toothed, jin, long; corolla tube lin. the limb 
of tive induplicate-valvate lobes; stamens five, e: d. June. ` 
l. entire, oblong or obovate, shining, slightly fleshy, i to 3in. 
en A petioles about jin. long, channelled above. A. 3ft. Chili, 
1815. (B. M. 2412; B. R. 299 
VETCH. See Vicia. no ue 
VETCH, BASTARD OR BLADDER. See 
Phaca. 
VETCH, BITTER. ‘See Orobus. 
x 
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