192 J. O. HAGSTKOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



P. nutans has been mixed up with P. nodosus and polygonifolius by several 

 earlier authors and many »natons-forms» belong to these species. 



The genuine 7iato?is- forms may be divided in the following varieties: 



Var. vulgaris Koch et Ziz: — » Folia late ovalia tripolhcaria* (= v. lacust- 

 ris Fries). 



Var. ovalifolius FiEBER: — »Folia ovato-oblonga* about 110x30 mm. 



Var. rotundifolius Brebisson: — sFeuilles larges, courtes, arrondies». 



Var. prolixus Koch: — » Folia oblongo-lanceolata*. Internodes and petioles, 

 besides, stretched (= v. jluviatilis Fries, 1828, non Schlecht., 1823), an adaption to 

 running water. 



Var. pymseus Gaudin is a small-leaved shallow-water form. 



Var. terrestris Gray is the terrestrial form of the species (= f. aiwphibius Fries). 



A small-leaved ovalifolhis-iovm I have named, in herbaria: 



f . pygmseoides n. f . : — Folia natantia 60 — 70 X 20 mm. 



On P. sparganifoUus which is the hybrid gramineus X natans, see below. 



The species has been figured innumerable times from the days of L. FucHSius (De 

 hist, stirp. comm. ins. 1542, 651.) up to the v^ery latest time. Figures to the ana- 

 tomy of stem and leaves etc. in C. RAUNKiaiR, De danske Blomsterpl., 1896, M. A. 

 Chrysler, The structure etc. 1907, t. XV, and C. W. Fontell, Beitriige etc. 1909, 

 t. V. f. 121 — 126; Hybernating organs in Graebner, Potamog. in Kikchner etc., 

 Lebensgeschichte etc. 1906, 427, f. 243. 



Distribution. In Sweden it is common through the whole country from Scania 

 up to the northern-most parts of Lapland, in Oland and Gothland, too (hb. Stock- 

 holm., Uppsal., Lund., Gothenb.). Likewise in Nonvay to sRebbenseson nord for 

 Tromso; sjelden nordligerc' : Blytt, Norges Fh I, 1902, 45; and Iceland, up to 

 Akureyri, 83, Stromfelt (hb. Uppsal.). Rtissia, Peninsula Kola. From thence to 

 Asia, Sibiria, Tungusk Jenisei, 76, Brenner (hb. Stockholm., Uppsal.). The north 

 boundary seems to coincide nearly with the year-isotherm-line of — 5° C. N. America 

 many stations (hb. Stockholm., Uppsal., Lund.) up to about the same isotherm. To 

 the south of this line it spreads through all countries down towards the equator, and 

 is said to occur also in South Africa, but I have seen no specimens. According to 

 P. DuSEN, Die Gefasspflanzen der Magellanslander, 1900, 234 — 235, P. natans is said 

 to be known from Chile and probably growing also in Fuegio orientalis at Cabo- 

 Pehas and »in dem Aysen-Thal an der Westkiiste von Patagonien», but I have seen 

 no P. natans from those regions. And it is a mistake when P. Graebner states: 

 y> sad- America: Patagonien (Dusen, det. Hagstrom)», Potamogetonacese 1907, 161. 



P. natans L. x polygonifolius Pourr. (P. gessnacensis Fischer, Die bayer. Pota- 

 mog. etc. 1907, 31, 42—43.) 



Var. Richtsfeldii Fisch., 1. c — F. hibernicus n. f. 



Caulis metralis, simplex tenuis. Folia submersa tenuia angustissima (1 mm) 

 longissima; emersa tenuia lanceolata 50—60x15 — 17 mm, ca. 15— 17-nervia, petiolis 



