SS Se ee 
ON LEMNACEA AND THE RAPHIDIAN CHARACTER. 13 
ticed in the fourth 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 
Lemna, 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 Pistia and Pontederacee. The 
calyptrate covering of the rootlets is beautiful in Pontederia crassipes 
and P. azurea ; and, of Pistia, besides the rootlet-sheaths, there is a 
larger sheath on the tip of the root-axis. 
Raphides.—'These are small and fragile in Lemna. In the fourth 
volume of this Journal I have depicted the raphidian diagnosis between 
L. minor and Wolfia arrhiza. And after a careful examination of 
several preserved specimens of two species of Wolfia from Portugal 
and Angola, courteously sent to me by the eminent botanist Dr. Wel- 
witsch, the exraphidian character was found very remarkable in every 
one of them. In some dried and colourless specimens of Lemna minor 
and Z. Angolensis of the same collection, the fronds were so shrivelled, 
their cells failing 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 were afterwards plainly brought into 
view, by thoroughly drying suitable and macerated fragments of the 
plants under pressure between glasses, then treating the preparation 
with 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 Wolfia arrhiza 
growing among Lemna minor, L. trisulea, 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 Lemne invariably presented their bundles of 
raphides, while the Wolfia 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 
Lemnacee, 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. 
