192 J. O. HAGSTEÖM, CRITICAL RESEARCUES ON THE POTAMOGETONS. 



P. natans lias been mixed up with P. nodosus and polygonijolius b} 7 several 

 earlier authors and many »natans-ioims» belong to these species. 



The genuine natans-iorms may be divided in the following varieties: 



Var. vulgaris Kocii et Ziz: — >Folia late ovalia tripollicaria» (= v. lacust- 

 ris Fries). 



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



Var. rotundifolius BeÉBISSON: — »Feuilles larges, courtes, arrondies». 



Var. prolixus K och: — »Folia oblongo-lanceolata». Internodes and petioles, 

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

 running water. 



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



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



A small-leaved ovalifoliits-iorm I have named, in herbaria: 



f. pygmeoides n. f . : — Folia natantia 60 — 70x20 mm. 



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



The species has l)een figured innumerable times from the days of L. Frciisius (De 

 lust. stirp. comm. ins. 1542, 651.) up to the very latest time. Figures to the ana- 

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

 Chrysler, Tlie structure etc. 1907, t. XV, and C. W. Fontell, Beiträge etc 1909, 

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

 Lebensgeschichte etc. 1906, 427, f. 243. 



Distribution. In Siveden it is common through the whole countiy from Scania 

 1 1 j > to the northern-most parts of Lapland, in Oland and Golhland, too (hb. Stock- 

 holm., Uppsal., Lund., Gothenb.). Likewise in Norway to »Rebbenaesön nord for 

 Tromsö; sjelden nordligere» : Blytt, Norges Fl. I, 1902, 45; and Ieeland, up to 

 Akureyri, 83, Strömfelt (hb. Uppsal.), liussia, Peninsula Kola. From thence to 

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

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

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

 t lie south of this line it spreads through all countries down towards the cquator, and 

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

 P. Dusé.v, Die Gefässi)flan/.en der Magellansländer, 1900, 234—235, P. natans is said 

 to l>^ known from Chile and probably growing also in Fuegio oricntalis at ( 1 abo- 

 Penas and »in »lem Aysen-Thal an der Westkiiste von Patagonien >, but I have scen 

 no /'. natans from those regions. And it is a mistake when V. Graebner statcs: 

 Siid-Anif fira : Patagonien (DUSEN, det. HagSTRÖm)», Potamoget onace.t 1 l!H)7, 161. 



1*. natans L. x polygonifolius Pourr. (I*, gessnacensis Fisoher, Die bayer. Pota- 

 mog. etc. 1907, 31, 42 43.) 



Var. Richtsfeldii Fisoh., 1. o. — F. hibernicus n. f. 



Gaulia metralis, simplex tennis. Folia submersa tenuia angustissima (I mm) 

 longissima; emersa tenuia lanceolata 50 -60 15 17 mm, ca. 16— 17-nervia, petiolia 



