Bletia, and others, the rliizoma assumes simply the form of an ordinary
tuber, and in Vanilla, Dendrobium, Vanda, and others of a similar
nature there is no rhizoma, but the stem lengthens as in common
plants, from which there is nothing to distinguish it; some of the
species of Dendrobium are remarkable for having the pseudo-bulbous
form at one end of their stem, and the common state at the other,
as in D. crumenatum, &c. When such plants as Dendrobium Pierardi
grow very fast, in an atmosphere which suits them, their stems
will frequently branch, when the new branches throw out roots in
abundance from their base; in such cases the original branches are
equivalent to the rhizoma of the pseudo-bulbous species, and the secondary
branches to the pseudo-bulbs themselves.
The LEAVES are variable in many points of structure. Among
the terrestrial species it is most common for them to be thin, flat,
and distinctly traversed with strong parallel veins proceeding at equal
distances from the base to the apex, and sometimes giving them a
ribbed appearance; they sheath the stein by their base, which is sometimes
dilated into a cup capable of holding water. But from this the
variations are extremely great; the leaves are exceedingly succulent and
cellular in many species, especially those inhabiting the Cape of Good
Hope; in Oberonia their faces grow together and render them equitant;
in Brasavola, Luisia and others they roll up and grow together in
such a manner as to become terete; in most epiphytal kinds they
are coriaceous without any external appearance of veins; in the supposed
parasites they are reduced to mere scales. In all the ephiphytal species
they are distinctly articulated with the stem, from which they are thrown
off when dead; in most terrestrial kinds this articulation is very imperfect.
It is common for the leaves of epiphytes to have their ends
oblique and notched; this structure is not found in the terrestrial species.
Most commonly they sheath the stem more or less perfectly by their
base; but in Vanilla and many others there is no sheath whatever. In
all the terrestrial species the leaves form sheaths in the first instance,
and bracts afterwards, by the nondevelopement of the lamina, so that
gradations may be traced between the most highly developed leaves,
and mere scale-like bracts; this is particularly evident in numerous
Ophrydese.
The INFLORESCENCE is in all cases either terminal or axillary ; but
it often seems not to be so. Thus in some of the genus Dendrobium
the flowers appear in racemes springing from the back of the leaves at
the base ; in this case the inflorescence pierces through the sheath of
the leaf, which is pressed so close to the stem that there is no room for
the flowers to develope in the ordinary way. In other instances the flowers
are described as radical ; they are, however, in all such cases formed
in the axil of a scale or leaf stationed near the root. When, as in
Cycnoches, Catasetum sometimes, and others of like nature, the flowers
spring from the naked sides of the stem, they are not the less axillary on
that account, but merely appear after the fall of the leaves to which
they belong. It is frequently the nature of these plants to direct their
flower-stems downwards, so that if planted in the ground they bury their
flowers in the earth ; this arises from their being naturally inhabitants
of the branches of trees, from which their flowers hang down freely in
the air.
Their FLORAL ENVELOPES are constructed irregularly upon a ternary
type, and consist of three exterior and three interior pieces.
The exterior pieces are usually nearly equal, and less brightly
coloured than the interior ; but the two lateral ones are often of a somewhat
different form from the other, which is anterior as the flower is
placed upon the inflorescence when young, but which often becomes
posterior when the flower is expanded, in consequence of the flowerstalk
being twisted, or curved; these parts are occasionally united by their
edges into a long tube, as in Masdevallia, or the lateral ones adhere to
the unguis of the lip in various degrees, or two of them are consolidated
into one, as in Corycium and many others. Occasionally the intermediate
piece is prolonged at the back or base into one or two hollow spurs,
as in the genera Satyrium and Disa ; still more rarely the lateral pieces
are also spurred, as in Disperis. Various other less important modifications
of the exterior pieces occvir, but in all cases the whole number
three is present.
The interior pieces are usually three, never more ; but in the instances
of Monomeria and Aviceps the intermediate one only is present.