432 NAIADACE^E. [Potamogeton. 



quite entire, upper 2-7 in., obovate or oblong-lanceolate, obtuse, lower 

 sessile; stipules very variable, obtuse, not winged. Peduncles 2-7 in. 

 Drupelets ventrall y convex, dorsally f-circular, keeled. — Distrib. Europe 

 (Arctic), N. Asia, N.W. India, N. America. — Var. P. spathula'tus, Koch and 

 Ziz, almost connects this with P. poly yonifo' litis. — Perthshire. 



** Flowering-stem icith copious barren branches below ; tipper leaves usually 

 floating, broader than the lower submerged ones ; peduncles arillary and 

 terminal, many- and dense- fid. 



5. P. heterophyl'lus, Schreb. ; stem slender, submerged leaves linear- 

 lanceolate, stipules small, peduncle stout thickened upwards, dry drupelets 

 small 3-keeled, beak short. 



Pools and lakes, from Shetland to Hants and Kent ; ascends to 2,800 ft. in 

 Perthshire; Ireland, rare; fl. June-Sept — Stem 2-4 ft., terete, green or 

 reddish, much branched below. Submerged leaves 1-7 in., sessile, flaccid, 

 acuminate or cuspidate, floating or similar or oblong petioled and 

 coriaceous. Peduncles axillary and terminal. Drupelets -j^ in., ventrally 

 nearly straight, dorsally |-circular.— Distrib. Europe (Arctic), N. Asia, 

 N. America. 



P. heterophyl/ltjs proper ; leaves not amplexicaul almost flat, upper opposite 

 coriaceous floating. P. gramin'eus, Fries, Koch. 



Sub-sp. P. ni'tens, Weber ; much branched, leaves usually all submerged 

 alternate recurved undulate shining, peduncles less thickened upwards, 

 spike shorter, drupelets smaller. — Aberdeen to Northumbd., Anglesea, 

 Surrey ; Ireland, rare. 



6. P. lane e ola' tus, 8m. ; stem filiform fragile, leaves sessile straight 

 linear- or oblong-lanceolate obtuse entire translucent nerves fenestrate, 

 upper opposite petioled, stipules slender acuminate, peduncles short not 

 thickened upwards, spike very short, dry drupelets ventrally 3-toothed. 



Rivers, Anglesea, Cambridge ; Co. Down ; fl. July-Sept. — Resembles slender 

 forms of P. heterophyl'lus, but leaves darker green, very obtuse, fenestrate 

 all over ; peduncles very slender, and spike shortly ovoid. Drupelets £ 

 in., nearly straight dorsally, much rounded ventrally, with a ventral and 2 

 lateral teeth, beak ventral. 



7. P. lonchites, TucTcerm. ; stem stout, submerged' leaves alternate 

 very long straight strap-shaped 7-9-ribbed quite entire translucent, floating 

 or opposite oblong-lanceolate long-petioled, peduncle slightly thickened 

 upwards, spike short, dry drupelets obovoid dorsally 3-keeled, beak 

 short. 



Ireland, River Boyne ; fl. June-Sept. — Stems much longer and less branched 

 than in P. heterophyl'lus, and submerged leaves much longer, drupelets 

 larger more like those of P. flu'itans, cotyledonary end of embryo involute. 

 — Distrib. Canada and California to Mexico and Florida. — Fruit described 

 from American specimens. 



8. P. lu'cens, L. ; stem stout, leaves large subsessile all translucent 

 linear- or oblong-lanceolate cuspidate undulate serrulate upper opposite 



