KUNGL. SV. VET. AKADEMIENS HANDLINGAE. BAND 55. N:0 5. 117 



farther beneath than in P. mucronatus and are besides of a less prominent appearance. 

 Ligules 14 — 15-nerved in the front-field. 



Styles and stigmas do not differ from the type. The fruit has a more promin- 

 ent keel and is in general larger, 3 — 3,5 mm long; but there is also a microcarp 

 form, the fruit of which measures only 2,5 mm in length and is exceedingly like a 

 large-fruited P. pusillus. 



Just as in P. pusillus the stem prolongs itself, often dichotomously, from the 

 base of the primary spike and the involucral leaves are often tapering at base like 

 a stalk from a somewhat broader blade. Their structure nevertheless remains un- 

 varied, and the topmost involucral leaves are built as the lower ones. 



The propagating buds are considerably larger than, for instance, those of P. 

 pusillus, but otherwise developed after the same type. The inner leaves overreach 

 a little the sheaths. 



The species varies as to the length of the internodes, the leaf-width, the shape 

 of the leaf-apex, and the size of the fruit. Already Chamisso ascertained two forms : 

 contractus (== f. vulgaris Fisher, Bayer. Pot. etc. 1907, 102) and elongatus (= f. eloji- 

 gatus Fischer, I. c), Linneea 1827, 179. In both of those forms the leaf-width and 

 the apex vary a little (see Fieber, Pot. Bohm. !). Forma i?isolitus Tiselius, Pot. 

 suec. exs. Ill 1897, N:r 150, presents distincty interrupted spikes of three verticils. 



Distribution. Sweden, scattered, or in some counties pretty common, as far 

 as 63° N. Lat. Its northern limit in Finland, Sweden and Nonvay forms a line drawn 

 from Kuopio to Ornskoldsvik and southwestward to Drammen. Respecting its first 

 detection in Sweden it may be quoted from labels in the museums (hb. Stockholm., 

 Uppsal. et Lund.): (Ostro-Gothia) si Rochella sjon V^ rnil fran Linkoping 1812 

 Potamogeton nov. spec, mihi^, without signature, but the hand seems to be that 

 of Bishop Agardh; collector, however, probably D:r Wallman. (Halland) »Stora, 

 ubi pro Fl. suec. novum detexi 1814 sed ex temporis genio pro P. compresso in Fl. 

 Hall. habui»: E. Fries (hb. Uppsal.). — In Gothland it does not occur. 



In the museums (lib. Stockholm., Uppsal., Lund., Gothob.) the following Euro- 

 pean countries are represented: Denmarh, many localities. — England, Surrey und 

 E. Norfolk. — Scotland, Thornhill and Balgavies Loch. France, three stations. — ■ 

 Germany, several stations. — Bohemia. — Poland. — In the Old World as well as 

 in North America P. obtusifolius probably does not extend to the south beyond the 

 40th degree N. L. 



P. obtusifolius M. & K. x panoruiitauus Biv. (P. Sturrockii Ar. Bennett 

 in Scottish Naturalist, 1883, 28, ut subs'p. sub. P. pusillo L.). 



Bennett says of this plant: » somewhat the habit of obtusifolius M. & K.» and 

 that by rights. But not the habit only is like P. obtusifolius. The compressed 

 (1,5 : 1) stem as well as the brown midrib of the leaves and the great vittte at the 

 base of the ligules recall this species. Our assertion that the original P. Sturrockii 

 from Marlee Loch is a hybrid plant is also well founded. The thin stem, elongated 

 peduncles, narrow leaves etc. aim at P. panormitanus and jmsillus {P. irichoides is 



