ON LEMNACEZ AND THE RAPHIDIAN CHARACTER, 11 
epidermal cells of Z. Zrisulca are wavy or sinuous, while the margins 
of the underlying parenchymatous cells are straight or smooth ; so tha 
the epidermis so far answers to a ‘ colpenchyma,’ and the subjacent 
tissue to a ‘spheerenchyma.’ Thus Z. /risu/ca 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 
olffia. 
The epidermis of Z. ¢risulea 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 achromatie 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 will be distinctly seen 
covering the subjacent tissue. At least, I have never failed to find the 
epidermis of Z, £risulea 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 an anatomical and physiological point of view, I have sub- 
mitted the plant to examination by an independent and competent 
authority, and, by the kindness of Mr. Carruthers, am enabled to give 
his report, as follows :— 
“ British Museum, Nov. 30th, 1868. 
“I examined the specimens of L. ¢risudca, 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 vies: And is the carbonic acid gas 
obtained from the water in which it is dissolved by endosmose through 
the epidermis, while in the air the carbonie acid gas has direct access 
to the parenchyma of the leaf by the stomata ?" 
The bundles of raphides in Z. ¢risulea 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 distinet cell of their own ; but a 
nicer examination in the mature frond commonly fails to detect any 
other boundary to the space which contaius them than the surfaces of 
