IV 
Bletia, and others, the rhizoma 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, &e. When such plants as Dendrobium Pie- 
rardi 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 secon¬ 
dary 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, Hat, 
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 stem by their base, which is some¬ 
times 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 imper¬ 
fect. 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 
Ophrydeae. 
