226 J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOQETONS. 



f. elongatus Baagoe in herb. — Folia caul. subm. ca. 35 — 40x10—11 mm. 

 Internodia 300—350 mm longa. 



f. maritimus Tis., 1. c, n:o 42. — Folia caul, subm. ca. 40 (30—50) X 10 — 15 

 mm, basi cordata. 



Similar to the f. elongatus but the internodes of usual length. 



f. lacuum n. f. — Folia caul. subm. ca. 40 — 60 X 10 — 12 basi rotundata, apice 

 quam in prsecedente angustiora. 



f. brevipes n. f. — Folia caul. subm. 30 — 50 X 4 — 5 mm basi rotundata, ramea 

 minima; pedunculus brevissimus, 20 mm longus. 



This beautiful small-leaved form is only known from Upland, Svartsjolandet, 

 near Stockholm. 



f. obtusus n. f. — Folia caulina subm. basi cordata apice obtusa, parva ca. 

 25 — 35 X 10 mm. 



While all the other forms of this hybrid have cjramineusA\ke leaf-apexes this 

 form alone has the leaf-apexes rounded like those of P. perfoliatus. It is remarkable 

 that the last mentioned species as to the form of the leaf-apex so extremely seldom 

 predominates over P. gramineus. True specimens of this form are, namely, hitherto 

 found in only one locality (see below), but I have seen less certain specimens from 

 Russia also, "Petersburg insula Krestofsky» (hb. Stockholm.). 



Denmark, »Skive a. Jylland», 04, J. Baagoe (hb. J. O. Hagstrom), by the 

 collector taken for P. perfoliatus. 



■( subintermedius Hagstr. 



f. typiciis (Tis.): Folia caul, submersa 35 — 50 X 9—10 mm basi ovata— subcordata. 



Here I class together not only the proper f. typicus Tis., 1. c. n:o 34, but also 

 his f. speciosus, n:o 36, f. jemtlandicus, n:o 38, f. curvifolius (Hartm.) Tis., 1. c, n:o 

 37 and some other crosses, forming transitions to p subgramineus by slightly developed 

 floating leaves, scarcely differing from each other, . and all with the above stated 

 leaf-size. This form is in Germany considered to be the original P. heteropliyllus 

 lacustris Cham., but see Cham, in Linnsea, 1827, 205 — 207; rather P. nitens ^hetero- 

 pliyllus Fries, which however certainly comprises many different forms. — This 

 intermediate form may be the commonest of all, at least in Sweden. 



f. mffilarensis Tis., 1. c. n:o 35: — Folia caul. subm. lanceolata, 70—100x7—10 

 mm, basi subovata. 



The plant from the Nossen Lake in Smoland (Sweden), P. Lundii Right., PI. 

 eur. I 1890, 13, which S. Almquist in Hartman, Handb. Skand. Fl. ed. 12, 1889, 

 49, has misdetermined and distributed as P. gramineus X prcelongus, coincides with 

 this f. mcelarensis Tis. and must be included with it. 



f. subsiniilis Tis., 1. c. n:o 39: — Folia caul. subm. aliquanto latiora, 65 — 80 

 X 12 — 14 mm, prseterea ut in prsecedente. 



f. intermedius (Tis.). P. niiens S intermedius Tis., 1. c. n:o 48. — Folia caul, 

 subm. 50—60x7 — 9 mm; spica floribus apertis remotis. 



