206 J. O. HAG3TRÖM, CR1TICAL KESEAKCHES OM T1IK POTAMOGETONS. 



bas not applied to hia herbarium, where thus no f. fluviatilis nor f. stagnalis etc. is 

 to be found, but only specimens named »P. gram. heter ophyHus». In Summa vegeta- 

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

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

 Nat. Hist. Museum, labelled, »in rivulis — — — Para?ciae Arjeploug Lappon. Pitens. 

 1824. L.est.» 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 Morong 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 an} 7 particular development of branches 

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

 to belong to the v. graminifolius and to »imitate P. alpina» with »towards both 

 (Mids less pointed lower leaves». All gramineus-f orms 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 grammens X perfoliatus. 



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 hia * heter ophyllus c. fluviatilis» 

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



The middle- and south-Swedish forms appearing in lakes, are by F&IBS classed 

 together under the »forma b. lactistris* (without floating leaves) and »formad, stagnalis» 

 (»with floating leaves and shorter submersed leaves). 



Beaide the land-form, f. terrestris Fries (»f. riparius» Fr. is probably a nitens- 

 form), Morong has establiahed a f. maximus, which according to the description as 

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

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

 and a f. longipedunculatus (Murat) with much stretched upper internodea and pedunoles 

 (as i ar as 20 — 25 cm). 



P. paucifolius Oi\ is according to Mkrtkns and Kocii a deep-water form with 

 elongated internodes and slightly developed floating leavea. 



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

 v. jlurialis Fries, partly other deep-water or laouatral forms which Fries oomprehended 

 under the name of »b. lacuslris , with shorter leaves an <l more branched slem. 

 The former occurs under three forma owing to (lie width of leaves: f. angustifoUu* 

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

 7—10 mm), and f. 8i vptentrionalia (Tis.) Hagstb. (leaves: 70—110 (160)xl€ 15 

 (27) min, see II ^.gstböm in Nia.MAN. Sveriges Ptora, 1001, 7961). Forma jcml- 

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



lcaved lacustris-t orms ; f . augcrmanirns Tl& isidentic with P. Wolfgangii, which, according 



