65 



NOTES ON PONDWEEDS. 



By Alfhed Fryer. 



(Plates 286 & 287.) 



Potamogeton falcatus Diihi. — Stem rouucl, slender, springing 

 from a tuberous rootstock ; branched from near the base with 

 distant alternate ascending branches, the lower of which are 

 permanently submerged, the upper ultimately rising to the surface. 

 Lower leaves alternate, amplexicfdd, flat, or slightly undulated at the 

 margin, e)itire, rarely longitudinally folded and recurved; elliptical 

 strap-shaped, gradually contracted from above the middle to the 

 somewhat rounded base ; apex acute or acuminate ; the midrib is 

 curved, and not quite central, so that many of the leaves are 

 straight on one margin and curved on the other : with one or two 

 rows of elongate cancellate areolations along the midrib, on each 

 side of which are three lateral ribs connected by a few indistinct 

 transverse veins. Upper leaves similar to the lower, amplexicaul, 

 even when opposite and subtending the peduncles, or rarely (on 

 the fruiting branches) stalked, floating, coriaceous, elliptical, with 

 12 opaque lateral ribs. Stijjules herbaceous, persistent, lower usually 

 small and narrow, ultimately not clasping the stem ; upper larger, 

 those at the base of the peduncles broad, stout, cymbiform. 

 Peduncles usually shorter than the subtending foliage, equal, or 

 only slightly swollen upwards in fruit, 1-1^ in. long. Fruiting spike 

 f-l in. long, cylindrical, dense ; drupelets small, dark green ; imier 

 margin rounded, terminated by the prominent subcentral beak ; 

 outer margin almost semicircular, acutelg keeled; lateral ridges dis- 

 tinct, distant from the central keel. Colour of the whole plant dark 

 green, or reddish green when young, drying darker, or blackish 

 green. 



When growing, P. falcatus in its early state has the habit and 

 appearance of the serratus-state of P. crispus ; later on, it resembles 

 long-leaved forms of P. heterophyllus, or luxuriant plants may 

 readily be mistaken for P. Zizii. When gathered, the young 

 plants are so exactly like certain forms of P. nitens that it 

 is difficult to find any specific difference. The difficulty of 

 ranging it under any already-defined segregate will, however, be 

 best explained by the following conflicting opinions I have been 

 favoured with by botanists who have made a special study of the 

 genus: — "Looks like crispus x rufescens"; "like an American form 

 of P. Zizii''; "Your plant is certainly a form of P. gramineus" ; 

 "^ heteropligllus form'' ; " ^-i nitens form " ; "■horealis ?" ; " Your plant 

 deserves a name." One more elaborate opinion I quote at length, 

 because it seems to me of great value as a clear statement of the 

 main difficulty to be overcome in establishing P. falcatus as a 

 species : — 



" I should not feel inclined to refer it to P. Zizii, nor do I see 

 anything which suggests to me hybridity ; I could not place it 

 under heterophyllus ; but I could, and feel disposed at present so to 

 do, place it under nitens. Unless the early and autumnal states of 



Journal of Botany. — Vol. 27 March, 1889.] f 



