136 J. O. HAGSTROM, CEITICAL RESEARCHES ON THE POTAMOGETONS. 



Floating leaves small, few-nerved. Pistils with the stigma on the ovary. Fruit 

 small. The anatomy of P. javanicus reminds, to a certain degree (see above), of 

 that of the Euhyhridi, namely as regards the stem prolongation, otherwise the 

 affinity of the two groups seems to be more external than essential. 



Series B. Nuttalliani Hagstr. 



Folia emersa multinervia; submersa 5-nervia evaginata, vaginis stipularibus 

 (ligulis) axillaribus fissis. Fructus majores rostro minimo apicali. — Herbee statura 

 robustiore. 



The two species belonging to this series occupy an intermediate place between 

 the small-grown, narrow-leaved groups and the following broader-leaved subsections. 

 Their distribution area seems also to be rather narrow, chiefly the same as that of 

 P. dimorflius Raf., or on the south spreading to the year-isotherm of + 18° C. 



Ser. A. EuhybrJdi Hagstr.. 

 P. dimorphiis Rafinesque. 



Monthly Magaz. and critical Review, 1817, 358. — P. diversifolius Barton, 

 Prodrom. fl. Philad. 1815, I, 27, e Raf. 1. c. — P. Zetterstedtii Wallman in Bot. 

 Zeit. 1843, 256 — 258. — P. Spirillus Tuckeeman, Amer. Journ. Sci. and Arts, 1848, 

 228. — Fig. 60, K, L; 61, D. 



We adopt the name P. dimorphus on account of Mr. Ar. Bennett's authority 

 (in litt., 1899 and 1900). Else we consider the name P. Zetterstedtii to concern, 

 positively, this species, to judge both from the original description and from plant 

 fragments with this name in the Univ. Mus. of Uppsala (coll. Dalman). The species 

 is recognizable by the roundedly obtuse, commonly more or less evidently ovate- 

 oblong to oblong, 7 — 11 -nerved floating leaves, the short obtuse submersed leaves, 

 the numerous small short-peduncled submersed spikes, the many-flowered rather 

 long-peduncled superior spikes and, especially, by the yellowish, shining, rounded 

 and beakless fruits, wholly lacking lateral keels but on the contrary with a promin- 

 ent crestlike dorsal keel. In the stem we find a few very thin subepidermal strands. 

 The species fruits richly. Some barren specimens I have seen are without doubt 

 the hybrid P. dimorphus X diversifolius. 



Distribution. N. America Charles ad Nattick, Mass., 79, Morong (hb. Stock- 

 holm.), In lacu Bantam, Conn., 83, Morong, Ashland, Mass., 83, Morong, In lacu 

 Spot, Mass., 81, Morong Chisago Lake, Minn., 92, Baltimore Taylor (all in hb. 

 Stockholm.), Maine, 81, Blake (hb. Lund.), Salem, Carolina, Dalman (hb. Uppsal., 

 see above!), N. Angl., Tuckerman (hb. Uppsal.), Pennsylvania, 84, Galen (hb. 

 Uppsal.). A specimen from Delaware, Canby, and another from S. Carolina, Curtis 

 (both in Uppsal.) might be the above said hybrid. — Canada, Que. and Ont. (hb. Haun.). 



