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12 ON LEMNACE^i; AND THE RAPIIIDIAN CHARACTKK.
the surrounding parenchymatous and epidermal cells; and so, too, of
the raphides of the other LemncB. The raphides of L. trisulca were
used in " Class-Botany " and histological demonstrations by Professor
J. 11. Balfour and Mr. George Lawsou some years before my descrip-
tion of these objects in the system of rajjhidian characters.
The root-sheaths of this plant are ciu'ved and sharp-pointed.
Lemna polyirJdza.—In this species the raphides are scanty. The
root-sheath is sharp at the tip.
Lemna gibba.—Kaphides scanty. Eoot-sheath with a bluntish point.
Lemna minor.—Bundles of raphides abundant, especially towartls
the edges of the frond. Starch-granules very plentiful. Hoot-sheath
with a blunt tip.
TFo^ffia arrliiza,—Destitute of raphides, by which character simply
this plant may be easily known from Lemna vimor. Starch-granules
plentiful, jDarticularly in the escaping and escaped bulbils ; stomata
very plain on these young bulbils.
Fig-. 1. Fig. 2. Fig. 3.
Fig. 1. Epidermis on the broad part of the frond of Lemna trisulca. The
epidermis j^asses immediately over a bundle of raphides.
Fig. 2. Epidermis on the narrow part of the frond of L. trisulca.
Fig. 3. Epidermis on the under side of the frond of L. minor, and passing
over a bundle of raphides.
Let us now review and elucidate some of these notes, and conclude
with the historical point.
Epidermis.—This tissue is present in the form of wavy-edged cells,
on both sides of the fronds of i. trisulca, and on the under as well as
on the upper side of the fronds of other Lemace.
Itool-sheaths.— Of these curious and charactciistic " pilcorhizcc," no-