432 NAIADACE^. [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 ventrally convex, dorsally ^-circular, keeled. DISTRIB. Europe 

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

 Ziz, almost connects this with P. polyyonifo'lius. Perthshire. 



** Flowering-stem, with copious barren branches belew ; upper leaves usually 

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

 terminal, many- and dense-fd. 



5. P. heterophyllus, 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 T ^ in., ventrally 

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

 N. America. 



P. HETEROPHYL'LUS 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. lanceola'tus, Sm. ; 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, TucJcerm. ; stem stout, submerged r 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 



