PotamogOon.] LXXVIIJ. NAIADEA. 429 



all the preceding species by the thread-like stems, and very narrow 

 linear leaves like those of Zannichdlia 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, under 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 in Britain. PL summer. 



[P. trichoides, Cham, and Schl., a European species found in the 

 eastern counties of England and in Ireland, is a form with capillary 

 stems, setaceous leaves, and very few flowers with solitary carpels.] 



11. P. pectinatus, Linn. (fig. 968). Fennel P. Sterna 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. pusUlut. 



In pools, ditches, and still waters, fresh or salt, almost all over the 

 world. Generally distributed over Britain. PL. summer. 



[P. Jiliformit, Nolte, a widely distributed species, in the north and 

 south hemispheres, has capillary leaves, flowers in whorls, and much 

 lamer nuts. It is not uncommon in Scotland, and has also been 

 found in Anglesea and Irelwd.] 



VI. SCHEUCHZEEIA. 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 reflezed 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 



