436 95. POTAMOGETONACE.E. 



2, WOLFFIA HorJcel. 



1. W. Michel' ii (Schleid.) ; fronds very small subglobidar 

 flattish above cellular beneath, solitary, young frond separating 

 immediately from the old one. Sy. E. B. 1398. R. vii. 14. W, 

 arrhiza (Wimm.) ed. viii. Frond like a grain of sand, subglobu- 

 lar at all ages, green. Offset from within the base of the old 

 frond. Fl. not seen in Europe. Ponds near London. A. E. 



Order XCY. POTAMOGETONACEJ3. 



Fl. perfect or imperfect. Perianth inferior, 4-parted, or 0. 

 Stam. free, 1, 2, or 4. Ovaries 4, distinct, each with 1 ovule 

 and 1 sessile stigma. Fr. a drupe enclosing a hard nut, or a 

 dry nut, not bursting, 1 -seeded. Albumen 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, with long stalks. Fl. 

 about 2 together. 



3. ZANNICHELLIA. Fl. monoecious, axillary. Barren with 

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

 perianth, persistent style, and peltate stigma. Nuts 2 5 

 or more, more or less stalked. 



1. POTAMOGE'TON x Linn. Pond weed. 



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

 free. 



1. P. ndtans (L.) ; upper 1. stalked coriaceous floating ovate 

 or elliptic folded at the base, petiole jointed a little below the limb, 

 low r er linear-lanceolate or setaceous,//*, (large) rounded on the 

 hack when fresh keeled when dry, peduncle equal. E. B. 1822. 

 R. vii. 50. St. creeping below, simple. Petioles plane-concave. 



1 See Mr. Fryer's magnificent Potamogetons of the British Isles, now 

 in course of publication, and his and Mr. Arthur Bennett's papers in the 

 Journal of Botany. We are much indebted to Mr. Fryer for assistance 

 with this genus and we have followed his views in adding several species; 



H.&J.G. 



