Acorus. | LXXVI. AROIDEE. 421 
Sedge.—A highly aromatic, reed-like plant, with a thick, shortly creeping 
rootstock. Leaves linear and erect, 2 or 3 feet long, about half an inch 
broad. Flowering-stem simple and erect, the long, linear, leaf-like spatha 
forming a flattened continuation, with the spike sessile at its base so as to 
appear lateral ; it is cylindrical, very dense, 2 to 3 inches long, of a yellowish- 
green colour. 
On the edges of lakes and streams, all over the north temperate zone, 
In Britain, believed to be indigenous only in some of the eastern counties 
of Engiand, but has been introduced elsewhere, and in Ireland and Scotland. 
Fl. summer, 
LXXVII. LEMNACEA, THE DUCKWEED FAMILY. 
A single genus, united by some with Aroidec, but anoma- 
lous in its mode of vegetation and very reduced flowers. 
I. LEMNA, DUCKWEED. 
- Floating plants, without distinct stems or real leaves, but consisting of 
small, leat-like fronds, either separate or cohering two or three together by 
their edges, emitting in most species one or more fibres from their under 
surface into the water, and multiplying by similar fronds growing out of 
their edges. Flowers very rare, appearing from a fissure in the edge or on 
the upper surface of the frond, and consisting of a minute membranous 
bract or spatha, enclosing 1 or 2 stamens, and a single 1-celled ovary, with 
one or more ovules, a short style, and no perianth. 
A small, widely distributed genus, 
Roots in clusters. Fronds above 3linesdiameter. . . . 4 ZL. polyrrhtza, 
Roots solitary. 
Fronds very thin, oblong or narrowed at one end (the young 
ones usually projecting on each side at right angles) . . 1. LZ. trisulea. 
Fronds broadly ovate, under 3 lines diameter. 
Fronds rather thick, slightly convex underneath . F . 2. L. minor, 
Fronds very thick and convex underneath 3. L. gibba. 
Roots none. pee minute, with the rece on the upper sur- 
face. ? ‘ 5. L. arrhiza. 
eA, L.. trisulca, fein (fig. 944). te Yy- ieobee Dupe: —Fronds very 
differently shaped from those of the other species, and much thinner. They 
are usually near 6 lines long and about half that breadth, thin, narrow 
and minutely toothed at one end, and ending in a little stalk at the other, 
with 2 young ones usually growing from opposite sides near the base, and 
a single root from underneath. Flowers of Z. ininor. 
On ponds and still waters. One of the common species on the Con- 
tinent, but less so in Britain, especially in the north. /#%. summer, but very 
rarely. 
2. G.minor, Linn. (fig. 945). Lesser Wy cniced —Fronds usually 
about 2 lines long, broadly ovate or orbicular, cohering 3 or 4 together, 
with one root under each but without any stalk, quite entire, and of a rather 
thick consistence. Ovary with a single ovule. 
On ponds and still waters, throughout the range of the genus, and gene- 
rally the commonest species, often covering the water to a great extent. 
Fl. summer, commencing early, and more easily met with in that state 
zhan any other species. 
3. G. gibba, Linn. (fig. 946). Gibbous Duckweed.—Fronds shaped 
