24 NATADACEAL 
in this country, and its minuteness is no doubt answerable for the fact that 
it has hitherto been recorded only from a few of the home counties. The — 
young plants are produced singly at the base of the old fronds, but soon 
detached. It is also known as Lemna michelii. 
Order XCIX. NAIADACEA—POND-WEED TRIBE. 
Flowers perfect, or imperfect; perianth either tubular, composed of 
scales, or wanting ; stamens free, 1, 2, or 4; ovaries 1-celled ; fruit either a 
hard nut, or a drupe enclosing a hard nut, l-seeded. This order consists of 
plants inhabiting ponds, streams, the sea, or salt-marshes ; their leaves some- 
times almost leathery, but more often thin and transparent, and the flowers 
small and green. 
1. PoND-WEED (Potamogéton).—F lowers in a spike; stamens and pistils 
in the same flower; perianth of 4 sepals ; stamens 2 or 4; carpels 4, sessile. 
Name from the Greek pétamos, a river, and geéton, a neighbour. 
2. Ruppia (Lippia).—Flowers about 2 on a stalk ; stamens and pistils in 
the same flower ; perianth none ; stamens 2; carpels 4, at first sessile, after- 
wards raised, each on a long stalk. Name from Henry Bernard Ruppius, a 
botanist of the last century. 
3. HoRNED POND-WEED (Zannichéllia).—F lowers axillary ; stamens and 
pistils in separate flowers; stamens 1; carpels 4—-6. Name from J. J. 
Zannichelli, a Venetian botanist. 
4, GRASS-WRACK (Zostéra).—Flowers composed of stamens or pistils 
separately arranged in two alternate rows, in a long leaf-like sheath ; perianth 
none. Name from the Greek zoster, a girdle, from its long riband-like leaves. 
5. Natas (Naias).—Flowers solitary or crowded, containing a single 
anther or a solitary carpel; leaves linear, either opposite, in bundles or 
whorled ; stipules attached to the base of the leaf. Name from the Greek 
Naias, a water-nymph. 
1. POND-WEED (Potamogéton). 
* Upper leaves floating. 
1. Broad-leaved Pond-weed (P. ndtans).—Upper leaves between 
oblong and egg-shaped, stalked, leathery, ribbed ; lower leaves linear, mem- 
branous, often wanting, or reduced to a mere stalk ; fruit keeled at the back. 
This, which is a very common plant in ponds, ditches, and slowly-moving 
waters, varies in size according to the depth of the water, scarcely having 
any submerged leaves in those which are shallow. The floating leaves are 
smooth, of a dull olive-green, and two or three inches long, on long stalks ; 
and the lower ones, when present, look like grass-leaves, and are sometimes a 
foot in length. The stem is round, and, in July and August, the cylindrical 
spikes of small green flowers rise above the surface of the pool. The roots 
are a favourite food of swans, and they are also eaten in Siberia by the 
peasantry. An old name for this plant was Water-spike ; the French call it 
Le Potamot. It is a common “river guest” in the waters of most European 
countries. 
