494 THE ALISMA FAMILY. 



7. Opposite Fond^reed. Fotamogeton densus, Linn. 



(Eng. Bot. t. 397.) 



Readily known by its numerous short leaves, aU opposite, and arranged in 

 two rows on opposite sides of the stem ; they are all submerged and thin, 

 broadly lanceolate, 6 to 9 lines long, folded and clasping the stem at their 

 base, with a strong midrib and 2 fainter parallel nerves, connected by a few 

 transverse veins. Stipules only under the peduncles or branches. Pe- 

 duncles very short, turned down after flowering, bearing a head of 2 or 3 

 flowers only. Ripe carpels rather large, rounded, and smooth. 



In shallow pools, and ditches, all over Europe, except the extreme north. 

 Common in Britain. Fl. summer. 



8. Slender Fondnreed. Fotamog'etoii pusillus, Linn. 

 (Eng. Bot. t. 215, P. compressus, t. 418, P. gramineus, t. 2,ibZ, P. tri- 



choides, Bab. Man.) 



Distinguished from all the preceding species by the thread-Uke stems, 

 and very narrow-linear leaves, hke those of Zannichellia or Ruppia, and 

 from the following 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 the Fennel P., 1 to 3 inches long and very seldom a line 

 broad. Peduncles slender, with a short, close spike of small flowers. Nuts 

 Bmall, ovoid, almost pointed, with a more or less strongly marked dorsal rib. 



In pools, ditches, and stiU. waters, fresh or salt, almost all over tlie world. 

 Common in Britain. Fl. summer. The P. acutifolius (Eng. Bot. Sujspl. t. 

 2609) and the P. zostermfolius (Suppl. t. 2685) appear to represent a robust 

 variety of this species, or the latter perhaps a state of the various-leaved P., 

 without the upper floating leaves. In both the leaves are S-nei-ved only. 



9. Fennel Fond'^eed. Fotamogeton pectinatus, Linn. 

 (Eng. Bot. t. 323. P.filiformis, Brit. FL) 



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 two small 

 scarious lobes, these scarious edges supposed to be stipules adhering to the 

 base of the leaf; the sheathing stipules of the other species either wholly 

 wanting or veiy rare under the peduncles. The midrib of the leaf some- 

 times separates into longitudinal, netted veins, only visible under a magni- 

 fying-glass, and there are usually 2 faint longitudinal nerves at some distance 

 from it. Peduncles usually bearing several clusters of 2 or 3 flowers, at 

 some distance from each other, forming a slender interrupted spike, rarely 

 reduced to a single, small terminal cluster. Nut as in the slender P. 



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

 Generally distributed over Britain. Fl. summer. 



LXXVIII. THE ALISMA FAMILY. ALISMACE^. 



Marsli or water plants, with radical leaves and leafless 

 flower-stems (except in Scheuclizeria). Plowers in terminal 

 umbels, panicles, or racemes. Periantli of 6 segments, either 



