POTAMO&ETOlf. ZAWNICHBIXIA. 385 



Spikes slightly interrupted. Back of fr. without] rgides and 

 roiinded when fresh ; nut with strong lateral ridges. Varying 

 greatly in length and size of st. and leaves. — P. marinus (Huds.J 

 has the stems naked helow. Sy. E. B. 1428. — Ponds and 

 streams. P. VI. VII. E.S.I. 



25. P. Jilifm-'mis (Pers.) ; I. Unear-setacecms 1-veined with 

 transverse veins, spikes greatly interrupted, fr. (I3 lin.) ohovate 

 rugose rounded on the hack mthovi keel or ridges when dry, nut 

 round-backed. — Sy. E. B. 1424. — L. like those of the preceding 

 but longer. Fr. smaller. Whorls very distant on the spikes. 

 Peduncles voy long. — Rare. Scotland. Lough Cullen and 

 Lough Oonn, Co. Mayo, Ii-eland. P. VL VIL S. L 



***** L. all opposite, submersed ; stipules none. 



26. P. den'sus (L.) ; I. all opposite pellucid clasping elliptic- 

 lanceolate or lanceolate, spikes shortly stalked ultimately re- 

 flexed. — E. B. 397. -ffi. vii. t. 28. — L. crowded, rather recurved. 

 Spike 4-flowered. Sep. triangular. — Ditches. P. VI. VII. 



E. S. I. 



2. Etjp'piA Linn. Tassel- Pondweed. 



1. B. marit'ima (L.) ; ped. long spirally twisted, anth.-cells 

 oblong I5 times as long as broad, nut ovoid rather obliquely 

 erect.— i?. B. 1-36. B. vii. 17. B. spiralis Hartm. — "Whole 

 plant stronger than the next. L. very narrowly linear, formed 

 as in Potamogeton pectinatus. S/ieaths large, inflated. — Salt 

 marshes in the South. P. VIL VIIL E. L 



2. B. rosteUdia (Koch) ; ped. short not spiral, anth.-cells 

 squarish as long as broad, nut gibbous at base obliquely ascend- 

 ing when young. — Sy. E. B. 1428. B. vii. 17. — Whole plant 

 very slender. L. rather filiform than linear. Sheaths small, 

 close.— Salt marshes. P. VL— VIIL E. S. I. 



3. Zamjtiohel'lia Linn. Horned Pondweed. 



1. Z.palus'tris (L.) ; style at least half as long as the diver- 

 gent nuts. — E. B. 1844. — Floating. L. slender, opposite, fili- 

 form. Fl. axillary, sessile. — a. Z, brachistemon (Gay) ; fr. 

 2 — 4 subsessile with crenate back, style 5 length of fr., stigma 

 large crenulate, anth. 2-celled. — fi. Z. macrostemon (Gay); 

 fr. 2 — 4 sessile rarely crenate, style 4 length of fr., stigma small 

 crenulate, anth. 4^eelled. — y. Z. pedicellata (Fr.) ; fr. 2 — 5 stalked 

 muricate, style as long as fr., stigma large crenulate, anth. 



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