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ON LEMXACEiE AND THE RAPHTDIAN CHARACTER. 11
epidermal cells of i. trisidca are wavy or siuuous, while tlie margins
of the underlying parenchymatous cells are straight or smooth ; so that
the epidermis so far answers to a ' colpenchyma,' and the subjacent
tissue to a ' sphccrenchyma.' Thus L. trisidca agrees with those other
species of the genus, which are well known to differ, as judiciously
described in ' English Botany,' in this form of epidermal cells, from
fFolJfi,:!.
Tiie epidermis of L. trisidca is so thin and pellucid as easily to
escape detection, and requires for a satisfactory examination a magni-
fying power of not less than two hundred diameters. If a suitable
fragment of the plant be placed under an achromatic object-glass of
one-eighth of an inch focal length, so as to show the parenchymatous
cells with the clearest definition, and the focus be then slightly length-
ened, the wavy edges of the epidermal cells wdl be distinctly seen
covering the subjacent tissue. At least, I have never failed to find the
epidermis of L. trisidca by this kind of procedure, and have often suc-
ceeded, by maceration and a little manipulation with needles, in sepa-
rating the epidermal cells from their underlying connection. But as
the question of the presence or absence of the epidermis is important,
both in au anatomical and physiological point of view, I have sub-
mitted the plant to examination by an independent and competent
authority, and, bv the kindness of Mr. Carruthers, am enabled to tjive
his report, as follows :
—
" British Museum, Nov. BOtli, 1868.
" I examined the specimens of L. trisidca, and saw distinctly the
epidermal cells which you figure, but I could not detect any stomata,
and I see you do not figure any. Does there exist in aquatic plants a
delicate epidermis destitute of stomata ? And is the carbonic acid gas
obtained from tiie water in which it is dissolved by endosmose through
the epidermis, while in the air the carbonic acid gas has direct access
to the parenchyma of the leaf by the stomata ?"
The bundles of raphides in L. trisidca are so evident, especially
towards the circumference of the frond, that they may be recognized
with the aid of a pocket lens. At first sight, under a higher magnify-
ing power, they seem to be within a distinct cell of their own ; but a
nicer examination in the mature frond commonly fails to detect any
other boundary to the space which contains them than the surfaces of