136 J. O. IIAQSTRÖM, CRITICAL RESEARCHES ON THE POTAMOOETONS. 



Fioating 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 Euhybridi, 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. Fruetus majores rostro minimo apicali. — Herbre 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. dimorphus Raf., or on the south spreading to the } T ear-isotherm of + 18° 0. 



Ser. A. Euhybridi Hagstr.. 

 P. (limorplms Rafinesque. 



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

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

 Zeit. 1843, 256 — 258. P. SpiriUus Tuckerman, Amer. Journ. Sci. and Arts, 1848, 

 228. — Fig. 60, K, L; 61, D. 



We adopt the name P. dimorphus on account of Mr. Ar. Bennet^s authority 

 (in litt., 1899 and 1900). Else \ve consider the name P. Zcttcrstcdlii 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 cvidently ovate- 

 oblong to oblong, 7 — 11-nerv-ed fioating leaves, the short obtuse submersed leaves, 

 the numerous small short-peduncled submersed spikes, the manv-flowered rathei 

 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 1 have scen are without donbf 

 i In' hybrid /'. dimorphus diversifolius. 



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

 liolni.), In lacu Bantam, Conn., 83, MOEONQ, Ashland, Mass., 83, Mobong, Iii laeu 



Spöt, M;iss.. 81, Mobong Chisago Lake, .Minn., 92, Baltimore Taylob (all in hb. 



Stockholm.), .Maine, Si, BLAKE (hb. Lund.), Salem, Carolina, Dai.mw (hb. Uppsal., 



above!), N. Angl., Tuckebman (hb. Uppsal.), Pennsylvania, 84, Galbb (hb. 



Uppsal.). A speeimen IVom Delaware, Canhy, and anothei' tioin S. ( 'arolina, Curtis 



(both in Uppsal.) mighl be the above said hybrid. — Oanada, Que. and Ont. (hb. Hann.). 



