sidered the principal inferior prolongation of the axis; thirdly, fleshy
simple or branched perennial bodies, much entangled, tortuous and
irregular in form, as in Corallorhiza, Neottia, &c. or nearly simple and
resembling tubers as in Gastrodia; and fourthly of perennial round
shoots, simple or a little branched, capable of extension, protruded
from the stem into the air, adapted to adhering to other bodies, and
formed of a woody and vascular axis covered with cellular tissue, ot
which the subcutaneous layer is often green and composed of large
reticulated cells. The points of these roots are usually green, but
sometimes red or yellow. In a very few instances of leafless species,
as Chiloschista usneoides, they become entirely green, and then appear
to perform the functions of leaves.
The STEM is found in its most simple state in the terrestrial Ophrydeffi,
where it is only a growing point, surrounded by scales and constituting
a leaf-bud when at rest, which eventually grows into a secondary
stern or branch, on which the leaves and flowers are developed
This kind of stem usually forms every year a lateral bud with a tubercular
root at its lower end, and, having unfolded its flowers and ripened
its fruit, perishes, to be succeeded by the stem belonging to the lateral
bud previously prepared ; hence those species to which this kind of stem
belongs have a l w a y s a pair of tubercles, one shrivelling and in progress of
exhaustion, the other swelling and in progress of completion. It is sometimes
found that the successive formation and destruction of annual tubercles
takes place beneath an equal number of skins, the new bud and tubercular
root being always formed within the axil of a scale-like coating
belonging to the parent; this takes place in the genus Thelymitra and
elsewhere. Sometimes such a stem, instead of forming a new bud upon
its side, pushes out a slender subterranean root-like runner, which, after
growing to some length, is arrested in its growth, and then forms at its
extremity a new bud, which lengthens at its base into a tubercle. In such
instances as this a kind of locomotion may be correctly said to take place,
the plant shifting its place yearly, and to such a distance as may be
determined by the length of the runner, which separates the parent
plant that perishes from the young offspring which is generated. Instances
of this are common in terrestrial genera. A modification of it
is when the tubercles are buried deep under ground, and always emit
a root-like stem upwards, which produces true roots until it reaches the
light and then only developes leaves. This occurs in Corysanthes and
elsewhere.
In other eases the growing point becomes perennial, thickens, is
scarred with the remains of leaves which once grew upon it, and
assumes the state of a short, round, or ovate, perennial stem or pseudobulb.
In such a case it commonly emits from its base a short shoot,
which creeps along the ground, or over the surface of a branch if the
species is an epiphyte, and becomes a woody rhizoma, covered with
scales which represent undeveloped leaves; after having advanced to a
length which varies in different species, the rhizoma ceases to grow,
and forms a new pseudo-bulb at its end. The latter subsequently protrudes
a new horizontal rhizoma, which again terminates in a pseudobulb,
and thus by degrees large masses of pseudo-bulbs are formed by
a single individual, and literally pave the place upon which they grow.
Such pseudo-bulbs are entirely analogous to the scaly bud found upon
the end of the tubercular root of an Ophrydea, and the rhizoma in like
manner is of the same nature as the runner that connects the old
tubercle with the new one in such a plant; but pseudo-bulbs, in consequence
of their perennial nature, are more completely formed, often have
a woody texture, generally a hard cuticle, assume various angular or
other figures, and develope a definite number of leaves from their points.
This is the common mode of growth of the genera Maxillaria, Stanhopea,
and many others. Pseudo-bulbs of this kind are always composed of
cellular tissue, containing a great quantity of mucilage (and, sometimes,
amylaceous granules,) traversed by simple fibro-vascular cords, and
hollowed into an infinite number of minute chambers. In Pholidota
imbricata the pseudo-bulb is pierced by a plexus of large brown laticiferous
vessels, in which I have not remarked a cyclosis, but whose particles
have an active motion on their own axis. In other cases the rhizoma,
instead of having pseudo-bulbs, forms short stems which are terminated
by one or more leaves, as in Pleurothallis and its allies, and in the genus
Cattleya and others; these differ from the pseudo-bulbous species only
in the thickness and form of their axis. The formation of tubercles and
terminal buds, or of creeping rhizomata and pseudo-b"ibs, is the most
common tendency of the order, but not the only one; in Eulopliia,