appear in the form of a fine downiness. An examination of the anatomical structure of this part
has revealed some facts which deserve to be described.
Let the dissections at the bottom of the plate represent very thin vertical slices of the thick
base of the lip, magnified about 500 times in diameter. A shews the appearance of the tubercular
lining, three of the glittering callosities being cut through ; they consist of cellular tissue arranged
with great regularity, and there is no distinct cuticle, but the thickness of the sides of the exterior
cells is greater than that of the interior ; some of the cells are filled with yellow colouring matter
or chlorophyll of a granular nature, others contain a red fluid (1, 1) ; the yellow in the cells next
the surface (2, 2) is paler and less granular than that in the inner cells (3, 3); cells still further
from the surface (4) gradually contain less granular matter, which appears to stick exclusively to
the sides, and not to float in the interior.------ B represents a similar view of the tissue forming the
outer surface, at a part where the colour is uniformly yellow; the whole of the cells contain
exclusively yellow granular matter, which becomes less dense as you proceed from the surface (4)
towards the interior (5); here also there is no distinct cuticle, or layer of empty cells; the surface
is covered closely with conical cells, which form the almost invisible downiness of that part.____ C is
a similar view of the same part, at a place where the colour is both yellow and purple; it is more
magnified; in this case it is seen' that the colouring matter is distinctly separated into separate cells,
and that the colour of one does not interfere with that of the other, but that the yellow is lodged
in one cell (1, 5) and the purple in others (4); the hairs themselves are sometimes filled with purple
fluid, as at 3; sometimes they are almost colourless, as at 4 ; or they are stained yellow, by the
addition of grumous matter of that colour to their interior, as at 1. At 3. it is seen that the hairs
occasionally grow together at the base.
Thus it appears that the varying tints of colour which are found in flowers are not produced by
colours proper to the tissue of which they are composed, or by a confused mixture of colouring
matter below the surface, but are caused by different colours, separately deposited in separate cells,
which are themselves uniformly colourless; I could not perceive that any of the yellow was ever
developed in the purple cells, and certainly the reverse did not exist; now and then yellow colour
appeared to come from the interior of a purple cell, but this I believe was owing to a purple cell
being placed between the eye and a yellow cell. These facts are in accordance with what has
been observed by Botanists in other cases.
The yellow cells uniformly presented a grumous or granular appearance, in consequence of
their chlorophyll being collected into irregular spherules of various sizes, but I could not succeed
in detecting any amylaceous matter in the interior of the spherules. The effect of applying tincture
of iodine was to destroy the brilliant orange yellow, and to convert it into that dull olive brown which
usually follows the application of this agent to the resinous secretions of plants, but I sought in vain
for any sign of blue in the interior of the granules. In one case, however, I remarked a small portion
of the membrane of a cell stained blue, much in the same way as is represented in Link’s leones
Anatomical, tab. xvi. fig. 13. in the tubercle of Salep. The application of dilute sulphuric acid
coagulated the yellow granules into a ball in the middle of each cell, and changed their colour to an
olive green.
While the yellow colour appeared to be entirely produced by the presence of matter in a
granular state floating in colourless fluid, the purple was in many cells as uniformly caused by
a purple fluid without granules; but in the deepest coloured cells, as at C 2, and 3, there was
evidently a tendency to granulation, although, when the contents were pressed out of such cells no
distinct granules could be found. Iodine produces no other effect upon the purple than to render
its colour less brilliant; but diluted sulphuric acid, without discharging the colour, renders it distinctly
grumous. I do not know whether this effect is produced by the acid coagulating the purple
chlorophyll, or whether it merely renders distinct and firm that which was previously semifluid and
undistinguishable. I am however persuaded that the amylaceous centres, round which Professor
Mohl conceives the chlorophyll to mould itself in the interior of vegetable tissue, do not exist in
this instance.
It has been stated, that there is no distinct cuticle to be found in this part of the Stanhopea;
that is to say, there is no membrane, composed of empty cells, which can be discovered either by
tearing it off, or by a vertical section ; such indeed is a general fact in petals and petaloid parts. It
is probable that in these organs its place is supplied by a great thickening and developement of that
external homogeneous membrane, first noticed by M. Adolphe Brongniart, afterwards found by
Professor Henslow, and subsequently described by myself and others. That it exists in a state of
great toughness, in very delicate flowers, has lately been shewn by me in Hydroteenia Meleagris, and
in this Stanhopea it is also present, although I did not succeed in detaching it. In general it
adheres so firmly to the cells it lies upon, that it merely adds to their thickness, as is shewn at A, B,
and C, and cannot be distinguished. But it also rises above the surface in the form of hairs, and
then the cell itself has no adhesion to it, but appears in the form of a lax, shrivelled, internal
membraneous sac, as at B 2, and elsewhere in that figure; the cell however, if filled with fluid,
extends so as to fill the whole cavity of the hair, as at C 3. In this latter case the membrane
adapts itself to the surface of the cells, and may be distinctly seen at their angles.
Possibly the hairs of plants are generally formed in this way; namely, of homogeneous cuticular
membrane, covering cells free at the sides, and only adhering to the parenchyma at the base. I am
led to this supposition from comparing the hairs of Stanhopea, Tradescantia, Campanula Rapuncuius,
Polystachya luteola, and others of like nature, all of which are evidently formed upon the same
plan, and in which it is probable that the phenomena of circulation may be observed. In these hairs
there is always a nucleus (B 3), in the inside of a sac or cell, which latter distends when wet, and
contracts afterwards, or after death, then leaving a considerable space between its sides and those
of the hair (B 1). It is in this space, which, when the hair is full of life, is extremely small, that
the motion of the fluids takes place, as is manifest in Tradescantia and Campanula Rapunculus.
I have not, indeed, succeeded in seeing any circulation in the hairs of Stanhopea; but when they
are killed by iodine the inner sac contracts and becomes more distinct, and then appear on the
outside of the sac, especially between its end and the point of the hair, evident traces of a
reticulation, which may be supposed to be a plexus of capillary laticiferous vessels, whose contents
are coagulated by the action of iodine.
Fig. D. represents a portion of the mesochilium, with the horns and part of the epichilium cut
off; this figure is given for the purpose of shewing the foramen that exists between the bases of the
two horns, and the nature of which is at present unknown.