48 J. O. HAQSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



finer, hairlike leaves. Absent in our Museums it seems, however, to be rather com- 

 mon southward. P. Graebner states: »nicht selten» (Synopsis etc. 1913, 540). 



f. ostiarius n. f. — Caulis fere capillaceus; folia elongata, 1 mm circ. lata; vagince 

 longissimse (ad 50 mm). 



This form is noticeable for its long leaves and sheaths; we suppose a local 

 adaption to the outlets of great rivers, since it is observed in /wtZm, »Gangetic Delta, 

 Province Bahar, River Gandak near Patna, 1857. Schlagintweit n:o 12981 » (hb. 

 Stockholm.) and in the estuary of Yenisei (coll. Brenner, Lundstrom, and Arnell 

 1875—1876, hb. Stockholm.). 



f. protensus Wallr., Sched. crit. 1822, 67. — P. pectinahis var. C. vulgaris 

 Cham, et Schl. 1. c. 1827, 165. 



Undoubtedly the most common form of all. Wallroth records it only from 

 rivers, but it is also met with in lakes and along the coast of the sea and elsewhere. 

 It is characterized by the stretched internodes and debile leaves (»foliis debilibus»), 

 and may be considered as a deep-water form. 



f. longlpedunciilatus TiSEL., Pot. suec. exsicc. Ill, 1897, n. 131: — Pedunculus 

 longissimus, 25 — 50 cm. Spica internodio infimo 30—50 mm longo. Ceterum ut in 

 prsecedente. 



A strongly marked deep-water form adapted to lakes, observed in Sweden in 

 the Baltic Sea at several places, for instance Uppland, Grisslehamn, 83, Hedlund 

 (hb. Uppsal.), Vjirmdo, 90, Thedenius (hb. Lund.), Stockholm, Saltsjobaden, 04, 

 Kjellberg (hb. Lund.), Sudermania, Dalaro, 83 Tiselius (hb. Stockholm., Uppsal., 

 Gotenb.). 



f. spissiis TiSEL., Pot. suec. exsicc. Ill, 1897, 127: — Caulis a basi usque ad 

 pedunculum ramosissimus. Folia inferiora caulina saepe magis quam 1 mm lata. 



Shallow-water form on muddy ground: Seen only from the original station, at 

 Stockholm, Varmdon, Bo, 91, TiSELitrs (hb. Stockholm., Uppsal., Lund., Gotenb.). 



f. scoparius Wallr., Sched. crit. 1822, 67: — »Caulibus prselongis — — — su- 

 perne in ramulos scopasformes polyphyllos expansis» etc. 



This form is also a modification belonging to shallow water, where the upper 

 internodes grow very short. The form is by many authors considered to be the true 

 P. fectinatus L. It is very likely so, though it may be supposed that Linnb's ma- 

 terial may have been very scanty, since he had not observed the leaf sheaths. 



The Museums contain this form from several stations, among others: Warwick, 

 England, coll. by Babington and by him labelled: P. jlabellahis (hb. Uppsal.). 



f. subdrupaceus FiscHER, Die bayer. Potamog. 1907, 125: — A form scoparius 

 but with more conspicuous rostrum on the ripe fruit. A specimen from "Bayern, 

 Bamberg, 02, G. Fischer » is preserved in hb. Stockholm, and by the author him- 

 self labelled sv. scoparius Wallr. f. suhdrupaceus Fischer ». 



f. iiiterruptus (KiT.) AscH. — P. interruptus Kitaibel in Schultes, Oesterreichs 

 Flora 1814, 328. — P. pectinaius b) interruptus (Kit.) Ascherson, Fl. Prov. Brand. 

 1864, 666. — P. flabellatus Babington, Manual Brit. Bot. 1851, 343. — P. vaginalis 

 Fischer, Verzeichn. Gef. pfl. Neuvorp. 1861, 40 ex Marsson, Fl. von Neu-Vorpomm. 



