48 J. O. HAGSTRÖM, CR1TICAL RESEARCHES ON THE POTAMOGETOKS. 



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; jolia elongata, 1 mm circ. lata; vagince 

 longissinue (ad 50 mm). 



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

 adaption to the outlets of great rivers, since it is observed in India, >Gangetic Delta, 

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

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

 1875—1876, hb. Stockholm.). 



f. protensos Wallr., Sched. crit. 1822, 67. — P. pec tinatus 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. longipeduneulatus Tisel., Pot. suec. exsicc. III, 1897, n. 131: — Pedunculns 

 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 Siveden in 

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

 (hb. Uppsal.), Värmdö, 90, Thedenius (hb. Lund.), Stockholm, Saltsjöbaden, 04, 

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

 Gotenb.). 



f. spissus Tisel., Pot. suec. exsicc. III, 1897, 127: — Caulis a basi usque ad 

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



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

 Stockholm, Värmdön, Bo, 91, Tiselius (hb. Stockholm., Uppsal., Lund., Gotenb.). 



f. scoparius Wallr., Sched. crit. 1822, 67: — >Caulibus pra?longis — — — su- 

 perne in ramulos scopacformes 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. pec ti iialus L. It is very likely so, though it may be supposed that Linné's ma- 

 terial may have been very scant}\ since he had not observed the leaf sheaths. 



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

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



f. subdrupaceus Fisciier, Die bayer. Potamog. 1907, 125: - A form scoparius 

 but with more conspicuons rostrum on the ripe fruit. A Bpeoimen from *Bayem, 

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

 self labelled »v. scoparius Wallr. f. subdrupaceus FlSOHER». 



f. iiitcrruptus (KlT.) ASOH. — P. inlerruplus KlTAEBEL in SoHULTBS, Oestenvichs 



Flora 1814, 328. — P. pectinalua b) inlerruplus (Kit.) Asciiersox, Fl. Prov. Brand. 

 L864, 666. /'. flabellalus Babington, .Manual Brit. Bot. 1851, 343. - /'. vaginalis 

 Fisoher, Verzeiohn. Gef. pfl. Neuvorp. 1861, 40 ex Marsson, Fl. von Neu-Vorpomm. 



