206 J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



has not applied to his herbarium, where thus no f. fluviatilis nor f. stagnalis etc. is 

 to be found, but only specimens named »P. gratn. heterophyllus » . In Summa vegeta- 

 bilium Scand. they are no more admitted, but on the other hand P. nigrescens is 

 kept as a separate species. The original specimen of this » species* is still in the 

 Nat. Hist. Museum, labelled, »in rivulis — — — Parseciee Arjeploug Lappon. Pitens. 

 1824. L^ST. » It is the well developed form occurring in shallow rivulets, ditches etc. 

 with slow current; it is endowed with floating leaves often with a little sloping base 

 (fol. — — — natantibus ovalibus in petiolum folia longiorem attenuatis: Fries, = P. 

 varians MoRO?irG in Fryer's herbarium) and rather large (in the original specimen 

 60 X 7 mm) submersed leaves, frequently turning dark in the press. Internodes short 

 and the plant usually richly branched, though the original specimens, being young 

 and low plants without spikes, do not present any particular development of branches 

 (subsimplex: Fr.). S. Almquist has, less correctly, considered the form probably 

 to belong to the v. graminifoUus and to »imitate P. aljmia" with »towards both 

 ends less pointed lower leaves ». All grajnineus-iorms have lanceolate, pointed, and a 

 little mucronate leaves, which property is so prominent that as to the apex it always 

 (or nearly so) predominates in the combination gramineus X ferjoliatus. 



A similar form occurs in streams with slow current: f. fluctuans Tiselius. 

 It has still larger submersed leaves, elongated internodes, and usually some large 

 floating leaves, sometimes very large, as much as 100 X 50 mm on petioles of 100 mm 

 in length and above. It grows likewise blackish in the press. Probably it was this 

 form that E. Fries had in view when establishing his 'heterophyllus c. fluviatilis-^ 

 which according to the author belongs to the south-Swedish streams (Nov. 2. p. 38). 



The middle- and south-Swedish forms appearing in lakes, are by Fries classed 

 together under the »forma b. lacustris^ (without floating leaves) and » forma d. stogmafe,s» 

 (nwith floating leaves and shorter submersed leaves). 



Beside the land-form, f. terrestris Fries (>f. riparius^ Fr. is probably a mte«s- 

 form), MoRONG has established a f. maximus, which according to the description as 

 well as to specimens in Morong's herbarium is rather many-shaped, a f. minimus, 

 a f. myriophyllus (Robb.) small-leaved and with extremely short rameal internodes, 

 and a f. Jongipedunculatus (Merat) with much stretched upper internodes and peduncles 

 (as far as 20—25 cm). 



P. paucifolius Op. is according to Mertens and Koch a deep-water form with 

 elongated internodes and slightly developed floating leaves. 



To the forms lacking floating leaves belong partly long-leaved river-forms, 

 V. fluvialis Fries, partly other deep-water or lacustral forms which Fries comprehended 

 under the name of »b. lacustris'>, with shorter leaves and more branched stem. 

 The former occurs under three forms owing to the width of leaves : f. angustifolius 

 Tis. (leaves: 70—110x4—5 mm), f. Wolfgangii (Kihlm.) Hagstr. (leaves: 70 — 110 

 x7 — 10 mm), and f. septentrionalis (Tis.) Hagstr. (leaves: 70 — 110 (160) X 10 — 15 

 (27) mm, see Hagstrom in Neuman, Sveriges Flora, 1901, 796!). Forma jemt- 

 landicus Tis. is a transitional form (stem-leaves 60—80 X 7—8 mm) to the shorter- 

 leaved Zac^isf?•is-forms ; f. angermanicusTis. is identic with P. Wolfgangii, which, according 



