350 94. POTAMOGETONACE^. 



inclosing a hard nut, or a dry nut, not bursting, 1-seeded. Albu- 

 men 0. Embryo with a thin skin having a lateral cleft. 



1. PoTAMOGETON. Fl. perfect. Perianth 4-parted. Anth. 

 4, sessile, opposite to the divisions of the perianth. Ovaries 

 4. Styles 0. Drupes 4, sessile. — Fl. sessile, spiked. 



2. RuppiA. Fl. perfect. Perianth 0. Stam. 2, the cells 

 considerably separated ; filaments very short, scalelike. 

 Ovaries 4. Styles 0. Nuts 4, vfith long stalks. — Fl. about 

 2 together. 



3. Zannichellia. Fl. imperfect, axillary. Barren with 1 

 stam., and no perianth. Fertile with a bellshaped perianth, 

 persistent style, and peltate stigma. Nuts 3 — 5 or more, 

 very shortly stalked. 



1. PoTAMOGETON IJun. Pondweed. 



* L. alternate, floral I. floating and sometimes opposite ; stipules 

 free. 



1. P. nutans (L.) ; 1. all stalked, upper coriaceous floating 

 ovate or elliptical plicate at the base, lower leafless petioles 

 linear or setaceous, fr. {large) rounded on the back when fresh 

 keeled when dry, peduncles equal. — E. B. 1822. R. vii. 60. — A 

 creeping rhizome. Lowermost 1. (phyllodes) often quite seta- 

 ceous ; upper 1. more or less cordate at the base, when pressed 

 flat a ridge is formed on each side of the base, jointed to their 

 stalks a Uttle below the limb. Petioles plane-concave above. 

 Sep. stalked, roundly rhomboidal. Anth.-cells not parallel. Fr. 

 greenish, I-2 — 2 lin. long. — Ponds, ditches, and slow streams. 

 P. VI. VII. 



2. P. polygonifolius (Pourr.) ; 1. all stalked, upper subcori- 

 aceous floating oblong-elliptical subcuspidate no leafless petioles, 

 lower 1. linear-lanceolate, fr. minute obtuse and rounded on the 

 back, peduncles equal. — P. oblongus Viv. E. B. S. 2849. — 

 St. creeping below. Petioles longer than leaves, plane-con- 

 cave above. Lower 1. often very narrow. Spikes rather short 

 and irregular. Sep. transversely elliptical, stalked. Fr. red- 

 dish, 1 , lin. long, having a faint keel and rather obscure lateral 

 ridges when dry. — Ditches, small streams, ponds. P. VII. 



3. P. plantagineus (Ducr.) ; I. all shortly stalked membranous 

 and pellucid blunt not cuspidate nor plicate, upper elliptical, 

 lower 1. oblong, fr. minute rounded on the back when fresh 

 keeled when dry, peduncles equal. — E. B. S. 2848. E. vii. 45. 

 — St. creeping below, branched, sometimes throwing out long 

 stoles from its upper axils. L. all beautifully transparent and 



