226 J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



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

 Internodia 300—350 mm longa. 



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

 quam in pra?cedente angustiora. 



f. brevipes n. f. — Folia caul. subm. 30 — 50x4—5 mm basi rotundata, ramea 

 minima; pedunculus brevissimus, 20 mm longus. 



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

 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 bybrid have graminetts-like leaf-apexes this 

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

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

 predominates över P. gramineus. True specimens of this form are, namcly, hitherto 

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

 llussia also, »Petersburg insula Krestofsky» (hb. Stockholm.). 



Denmark, »Skive å. Jylland*, 04, J. Baagöe (hb. J. O. Hagström), by the 

 collector taken for P. 'perfoliatus. 



v subintermedius Hagstr. 



f. typicns (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 

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

 37 and some other crosses, forming transitions to ,3 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. heterophyllus 

 lacustris Ciiam., but see Cham. in Linnaea, 1827, 205 — 207; rather P. nitens $ hetero- 

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

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



f. melarensis Tis., 1. c. n:o 35: — Folia caul. subm. lanceolata, 70— 100 x 7— 10 

 mm, basi subovata. 



The plant from the Nossen Lake in Smoland (Sweden), P. Lundii Riciit., Pl. 

 eur. I 1890, 13, which S. Ai.mquist in Hartman, Handb. Skand. Kl. ed. 12, 1889, 

 49, has misdetermined and distributed as P. gramineus x pralongus, coincides with 

 this f. madarensis Tis. and must be includcd with it. 



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

 X 12 — 14 min, praterea ut in prseoedente. 



f. Intormediua (Tis.). P. nitens o intermediua Tis., 1. c. n-.o 48. — Folia caul. 

 subm. 5d 60x7 — 9 mm; spica floribns apertis remotis. 



