<70 TETRANDRIA — TETRAGYNIA. [Potamogeton. 



10. P. prcclongus, yVvxW. (Jong-stalked Pond- Weed) ; leaves 

 oblong obtuse, witii 3 principal and several lesser parallel nerves 

 arising from the base connected by reticulations, peduncles elon- 

 gated, spikes cylindrical many-flowered. Cliam. in Linncca, v.'n. 

 p. 191. Reich. Iconngi: t. 185. — /3. foliis angustioribus. 



Lakes and pools, Berwickshire. Moss of Litie, Nairnsliire. Loch- 

 leven, along with /3. Fl. July. '^. — This is best distinguished by its 

 truly oblong (by no means elliptical) leaves, nerved from the base, where 

 they are semiamplexicaul, and by the lengthened /jer/^/«c/e. In size it 

 almost cqnals P. lucens. lleichenbach has given an admirable repre- 

 sentation of this species. 



***** Leaves alternate, tipper ones floating y broader than the 

 rest; stipules free. 



11. P. heterophijllus, Sclireb. (^various-leaved Pond-rceed) ; 

 *' upper leaves elliptical stalked floating slightly coriaceous, 

 lower ones lanceolate membranaceous sessile, flower-stalks 

 swelling upwards." B. Bot. t. 1285. 



Pools and ditches, in various parts of the country. Fl. June, July. 

 If. — 3Ir Wilson finds this sometimes without floating leaves, when it 

 seems intermediate between P. lanceolatus and P. rufescens. " The 

 stipules are not dorsally winged, short and broad, yet with 2 stout princijial 

 ribs, ovate and blunt ; both they, and the leaves subtending the flower- 

 stalk, ivideh/ spreading. Leaves distantly inserted on the stem ; upper 

 ones considerably larger than the rest. — Distinguished by these marks 

 and the clavate flower-stalk, from P. rufescens and lanceolatus." Wilson. 



111. P. lanceolatus, Sm. (lanceolate Pond-weed) ; submersed 

 leaves lanceolate tapering at the base membranaceous with about 

 r-) — 7 nerves and transverse veins, near the middle nerve are 

 small chain-like reticulations, floating leaves elliptic-lanceolate 

 subcoriaceous many-nerved petiolate, peduncle about as long as 

 the leaves, spikes elliptical. — ,5. floating leaves none. P. lanceo- 

 latus, E. Pot. t. 1985. 



Pools and ditches. — a. and /3. growing together in a rivulet in Angle- 

 sea. Angus-shire, Kincardineshire. In the Lossie, by Elgin. Fl. July. 

 %. — Tills plant had been very little understood tdl Mr Wilson found 

 it growing in a small rivulet in Anglesea, having a moderately swift 

 stream. " Floating leaves are alwcajs found where the current is slow. 

 The chain-like reticulations are only distinguishable near the mid-rib on 

 the submersed leaves, the floating leaves being elegantly^overspread by 

 them." ( Wilson in litt.) This is quite correct, and the portion of chain- 

 like reticulations increases gradually upwards. Tiie difficult}'^ is now to 

 distinguish this plant from the preceding, than which, however, it is much 

 smaller and more delicate in all its parts. Sir J. E. Smith considered 

 the P. setaccus of Linn, and Huds. and Fl. Brit, to be probably the 

 same as the present ; but this can hardly be. 



13. P. Tifescens, Schrad. (reddish Pond-7oeed) ; submersed 

 leaves lanceolate membranaceous many-nerved with connecting 

 veins and many linear reticulations at the midrib, floating ones 

 subcoriaceous on long stalks. Cham, et Schlecht. in LvmceUy v. 

 xup. 210 P.fluitans, E. Bot. t. 1286. 



