13 ON LEMNACEZ AND THE RAPHIDIAN CHARACTER. 
the surrounding parenchymatous and epidermal cells ; and so, too, of 
the raphides of the other Zemze. The raphides of L. trisulca were 
used in * Class-Botany ” and histological demonstrations by Professor 
J. H. Balfour and Mr. George Lawson some years before my descrip- 
tion of these objects in the system of raphidian characters. 
The root-sheaths of this plant are curved and sharp-pointed. 
Lemna polyrrhiza.—ln this species the raphides are scanty. ‘The 
root-sheath is sharp at the tip. 
Lemna gibba,—Raphides scanty. Root-sheath with a bluntish point. 
Lemna minor.—Bundles of raphides abundant, especially towards 
the edges of the frond. Starch-granules very plentiful. Root-sheath 
with a blunt tip. 
Wolffia arrhiza—Destitute of raphides, by which character simply 
this plant may be easily known from Lemna minor. Starch-granules 
plentiful, particularly in the escaping and escaped bulbils ; stomata 
very plain on these young bulbils. 
Fig. 2. 
Fig. 1. Epidermis on the broad part of the frond of Lemna trisulea. The 
epidermis passes 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 Z. 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 L. £risulca, and on the under as well as 
on the upper side of the fronds of other Lemne. 
Root-sheaths.—Of these curious and characteristic “ pileorhizze," no- 
