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ON lemnacea: and the RAPHIDIAN CHABACTER. 16
ticed in the fourtli volume of this Journal, there is neither an intelli-
gible figure nor mention in 'English Botany.' Of morphological pheno-
mena, the functional value may be none the less for its obscurity. In fresh
Lemrue, the root-sheaths afford some good specific characters, and should
be compared in all the species, native and foreign, as well as with the like
sheaths in other genera and Orders, as Pisiia and Po7itecleracea. The
calyptrate covering of the rootlets is beautiful in Fontedtria crassipes
and P. azurea ; and, of Pistia, besides tlie rootlet-sheaths, there is a
larger sheath on the tip of the root-axis.
Raphidts.—These are small and fragile in Lemna. In the fourth
volume of this Journal I have depicted theraphidian diagnosis between
L. minor and TFolffici arrhiza. And after a careful examination of
several preserved specimens of two species of Wolffia from Portugal
and Angola, courteously sent to me by the eminent botanist Dr. A\ el-
witsch, the exraphidian character was found very remarkable in every
one of them. In some dried and colourless specimens of Lemna minor
and L. Angolensis of the same collection, the fronds were so shrivelled,
their cells fiiiling to freshen out in water, and being beset and obscured
by adherent Diatoms, that the raphides escaped detection at first.
But bundles of these crystals Avere afterwards plainly brought into
view, by thoroughly drying suitable and macerated fragments of the
plants under pressure between glasses, then treating the preparation
witb turpentine, and subjecting it to a moderately high magnifying
power.
Of L. minor I have examined an immense number of fresh speci-
mens from various localities, and never failed to find the bundles of
raphides without the least difficulty. And having during this autumn
and in the month of November got a plentiful supply of IFolffia arrhiza
growing among Lemna minor, L. trimlca, and Riccia fluitans, in the
neighbourhood of Canterbury, I have repeatedly and diligently gone
over the examinations again, and always with the same positive results.
The fronds of the two Lemnce invariably presented their bundles of
raphides, while the IFolffia was as constantly destitute of them.
These results are the more interesting, as all the plants were brought
in the same bottle of water from one place, and thus confirm my for-
mer observations on the specific value of the raphidian character in
Lemnaceee, as well as the constancy of either the abundance, scarcity,
or total want of raphides in different species of such nearly allied plants
growing side by side in the very same pool.