Potamogeton. | LXXVIIT. NAIADEA. 429 
all the preceding species by the thread-like stems, and very narrow 
linear leaves like those of Zannichellia or Ruppia, and from the follow- 
ing by the scarious sheathing stipules, always observable in the axils 
of those leaves at least which are under the branches or peduncles. 
Leaves veined as in P. pectinatus, 1 to 3 inches long and very seldom a 
line broad. Peduncles slender, with a short, close spike of small flowers. 
Nuts ovoid, undeér 1 line long, almost pointed, with a more or less strongly 
marked dorsal rib. 
In pools, ditches, and still waters, fresh or salt, generally spread at 
least in the northern hemisphere. Common i in Britain. Fl. summer. 
[P. trichoides, Cham. and Schl., a European species found in the 
aces counties of England and in Ireland, is a form with capillary 
stems, setaceous leaves, and very few flowers with solitary carpels. ] 
odd, 'P. pectinatus, Linn. (fig. 968). Fennel P.—Stems thread-like, 
with very narrow, grass-like leaves, usually 2 or 3 inches long, most of 
them dilated at the base into a rather long sheath, which is scarious 
at the edge and often projecting at the top into 2 small scarious lobes 
(stipules adhering to the base of the leaf); the sheathing stipules of 
_ the other species either absent or very rare under the peduncles. The 
midrib of the leaf sometimes separates into longitudinal, netted veins, 
only visible when magnified, and there are usually 2 faint longitudinal 
nerves at some distance from it. Peduncles usually bearing several 
-distant clusters of 2-or 3 flowers, forming a slender interrupted 
spike, rarely reduced to a single, small terminal cluster. Nuts as in 
P, pusillus. 
In pools, ditches, and still waters, fresh or salt, almost all over the 
world. Generally distributed over Britain. Fl. summer. 
[P. filiformis, Nolte, a widely distributed species, in the north and 
south hemispheres, has capillary leaves, flowers in whorls, and much 
larger nuts. It is not uncommon in Scotland, and has also been 
found in Anglesea and Ireland.] 
VI. SCHEUCHZERIA. SCHEUCHZERIA. 
Erect marsh plant with few linear leaves, and a short, loose terminal 
raceme. Perianth-segments 6, small and equal, with an anther sessile at 
the base of each one. Carpels 3 to 6, each containing 1 or 2 seeds, and 
opening inwards by longitudinal slits. 
The genus is limited to the single British species, nearly related to 
Triglochin, and with it forming the distinct tribe of Juncaginece, by some 
regarded as a separate family. 
1. S. palustris, Linn. (fig. 969.) Marsh S.—A rush-like perennial, 
with a creeping rootstock, and an erect stem about a foot high. Leaves 
few, linear, sheathing at the base, then narrowed, and nearly cylindrical ; 
the lower ones often longer than the stem; the upper ones passing into 
short, sheathing floral bracts. Flowers few, rather small, on pedicels 
‘ about 6 lines long, forming a short, loose terminal raceme. Perianth 
slightly coloured, of 6 spreading or reflexed segments. Stamens 6. 
Carpels 3, rarely 4 to 6, nearly 3 lines diameter when ripe, opening by 
a longitudinal slit, and containing 1 or 2 seeds. 
In bogs and peaty marshes, in northern and Arctic Europe, Russian 
