26 NATADACEE 
a short spike, the stalk slightly thickened upwards. This is a rare species — 
found in the river Boyne, Ireland. It flowers from June to September. 
* * Leaves all submersed and pellucid. 
8. Curly Pond-weed (P. crispus).—Stem flattened, much branched ; 
leaves narrow, oblong, branched, sessile, serrate, usually wavy. This is one ’ 
of the commonest Pond-weeds of our ditches and rivers, bearing in June and 
July its short loose spikes of yellowish-green flowers. Its leaves are often 
very much frilled at the edge, and of a brighter green than many of the 
species. It is evidently a very favourite plant with ducks, and probably 
with many other water-fowl, both wild and domestic; and as its creeping 
stems penetrate the soft soil, it propagates itself so quickly that it would, if 
left unmolested, soon fill a pond or slow river. 
9. Perfoliate Pond-weed (P. perfolidtus).— Leaves heart-shaped, 
embracing the stem, uniformly membranaceous. This, too, is one of our 
commonest species, and its long slightly-branched stems occur in ponds and 
lakes. Its leaves are clear, and, when young, of a dull olive-green, becoming 
browner as they grow older, and appearing, when dried, as a thin brown 
membrane. The Rey. C. A. Johns remarks, that in their dry state they are 
so sensitive of moisture, that if laid on the palm of the hand they will curl 
up. The plant bears in July and August short oblong spikes of greenish 
flowers. 
10. Willow-leaved Pond-weed (P. salicifolius).—Leaves all trans- 
lucent, the submerged lance-shaped, half clasping; stems slender, rounded, 
slightly branched ; flower-spike short, its stalk not enlarged upwards. It 
flowers in July, and has been found in rivers in Herefordshire. 
ll. Griffth’s Pond-weed (P. griffithii)—Stem rounded, branched ; 
lower leaves strap-shaped, half clasping the stem, with hollow tip; upper 
leaves lance-shaped, tapering into a long leaf-stalk ; stipules blunt, long and 
slender ; spike dense, on a slender stalk which is shorter than the upper 
leaves. It flowers in summer, and has been found only at Llyn-an-Afon, in 
Carnarvonshire. 
12. Long-stalked Pond-weed (P. preléngus).—Leaves oblong, blunt, 
sessile, nerved from the lower part, and half-clasping ; flower-stalks very 
long; stipules large. This rare species is one of the largest of our Pond- 
weeds, and is fou’ad in some ditches and rivers chiefly in the north of this 
kingdom, forming in deep water large thick masses just below the surface. 
It has very long stems, and clear dark green leaves, but the stipules are 
white, tinged with red, and are very long. The plant is well distinguished 
by the thick stalks of its flower-spikes, which are from half a foot to a foot 
in length. It bears a cylindrical many-flowered spike in June and July. It 
occurs in rivers between Caithness, Essex and Shropshire, also rarely in Ireland. 
13. Long-leaved Pond-weed (P. longifélius).—Leaves very long and 
lanceolate, narrowing below ; stipules winged; common flower-stalks very 
long. This plant, which was found in Lough Corrib, Galway, has long 
slender stems, and pellucid entire leaves, with very short stalks, and green 
prominently-winged stipules. Its spike of flowers appears in July and August. 
14. Shining Pond-weed (P. licens).—Leaves between elliptical and 
