8 INTKODUCTORY ESSAY.
ridge on the side of the insertion of the spadices. As the spadices are
on the loaf-shcathsj and as the leaves, though really spirally disposed, are apparently
opposite, one internode has the ridge on one side, the next has it on the side opposite.
This ridge marks the course of the fibro-vascular bundles which pass into the
spadix or into its homologue the leaf-sheath flageilam. The fibro-vascuîar bundles
of one internode of the stem pass into the sheath next above, -which they traverse
througliout its length ; their coarse is marked by a slight longitudinal swelling
of the surfacc on the side which corresponds with the analogous swelling on
the internode ; this ridge usually ends near the mouth of the sheath where the spadix
is inserted.
The stems of Calami are usually rather spongy in the centre, and are always
very hai-d externally, though they are at the same time flexible and clastic. The
stems of Calami divested of thcii- slieaths have almost always a polished surface,
and look as if covered with a thin layer of vitreous varnish; sometimes, however,
the sui-face is opaque, but almost always is of a straw-yellow colour, especially
when dry. This vitreous appearance of the naked canes of many Calami is due to
the presence of a very thin layer of a silicious substance which entirely covers
them.
When the stem of a Calamus, more piii'ticularly of one that has a very
polished and shining surface, is bent, small thin lamella; maj^ be seen to craok oS
as the result of the fractui-e of the thin coating of siHcious material with which the
cuticle of the stem is laden. In these lamella; no eeilular structure whatever can
be made out. The cells which constitute the epidermal layer of the stem, and
immediately underlie this cuticle, are also more or less laden with silica, frequently
to such an extent that even after incineration they retain their form and preserve
their minutest details, so that even the charactei-istie structure of the stomatie cells
continues unaltered. The histological elements of the inner part of the stem are
however, only very partially silicised.
This abundaut silicious secretion in the tissues of l^alms suggests to my mind
the hypothesis that the frequency with which the wood of Palms is found silicised
in a fossil state may not depend entirely on a molecular substitution of silica for
cellulose In the wall of their cells, but may also be due to the excessive
impregnation of that substance which probably already existed during life in the
tissues of the Palms of past ages.
The more polished and vitreous the surface of a stem is, the more it is
impregnated with silica and the ni.oro it is valued for economic purposes. In the
category of species whose stems are thus valuable are ineludod 0. msius, 0.
optmv3, 0. tmuis, C. Rotang, etc.
IV.—The Leaves.
The leaves or frond» of scandent Calmni often appear at first sight alternate,
owing to their being separated from each other by considerable intervafe because of
the elongated character of the internodes. When, however, the loaves are closer
together, as is the case near the apex of the stem where they form a more or
less dense crown, a spiral tristichous arrangement is quite obvious.
THI LKATES.
A complete CulamuB leaf is made up of a basilar portion or sheath, which usuaUy
takes the form of a tube completely enclosing each joint or internode, and of the
leaf proper. Within the latter we have to distinguish a medium portion or rib
known as the rachis, and to right and left of the rachis the leaflets, which vary
in number according to the species. The first or lower portion of tho rachis which
usually is destitute of leaflets may be held to represent the petiole. Then in
whole groups of species the rachis is prolonged beyond the distal leaflets as a long
and slender whip-like clawed appendage termed tho cirrus.
The leaves of an adult Caltiims plant are always pinnate except in the cases
of C JlahlMus where they are furcate-flabellate, in that of 0. mjiatus where they
are digitate-radiate and in those of 0. dijitaius and 0. packs^Umo,«, where we
find only 3—4 leaflets approximated at the apex of tho petiole. These three kinds
of leaves however, are, it is to be noted, kinds that first appear after the
gemnination of the seed, even in those speeies that ultimately have regularly piunate
leaves in the higher part of the plant.
On aecount of the diversity of form assumed by the loaves in Oalamia it is
therefore most important to know when describing them whether they be leaves
from the lower or leaves from the upper part of the plant, because the diflerences
between leaves from these two situations are often very remarkable. I have
therefore in these descriptions of Calami, unless it is otherwise stated, always record,
ed the characters of the leaves of the adult plant.
In the measurements given by me of the leaves of Calamus it is to be noted
that I include in the leaf that portion of the rachis which has no leaflets and
which is usually spoken of as the petiole. But the sheath is not included nor
is the terminal cirrus, when a cirrus is present; so that the length of the leaves
is measured along the rachis from its junction with the sheath to the point of
attachment of the uppermost leaflets.
As tho fii-st leaves in a very young plant of Oalamu, are flabellate, furcate,
radiate or digitate, we may conclude that the phinate leaves of the lull grown plant
are dérivâtes of these simpler forms and consider 0. iifitatus, C. paohjsUmmus, C.
radiatm and C. fiaielUtus as survivals of the primitive types of the genus.
The cirrus is often very long and is always armed with "claws." These
claws, as we have already seen in discussing them generally, are sometimes sohtary,
but are more frequently 3-nate or 5-nate.digitate, especially towards the tip of the
cirrus and in more robust cirri are even 7-nate and arranged in 1 - | whorls
with more or less uniform naked intervals between the groups of claws. In
appearance and in function the cirrus corresponds exactly to the leaf-sheath flagellum,
to bo discussed further on: in origin, however, it is altogether diBerent.
In cirriferons leaves the leaflets attached along both sides of the rachis may
either cease abruptly at a definite point or may gradually decrease in size upwards.
The leaves of the lower part of the stem and the radical leaves are noncirrifereus,
and often end in two mere or less confinent leaflets or in bifurcate
leaflets even in species where the leaves in the higher part of the plant
normally have a typical cirrus.
ANN. EOY, BOT. GARD. CALCUTTA, VOL. X I .