KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. NIO 5. 139 



linearibus acutis, sessilibus, emersis oblongo-ovalibus natantibus, spicis cylindricis. 

 In Carolina et Delaware.» P. capillaceus Poir. seems otherwise to be the earliest 

 name being unquestionable and employable. 



Chamisso and Schlechtendal have correctly described the floating leaves of 

 this species: — »utrinque acuta apice ipso obtuso paululum brevissime producto» 

 (Linnaea 1827, 208). The marginal lines, you will observe, meet under more or less 

 acute angles, whereas the preceding three species alvvays have more or less roundedly 

 obtuse floating leaves. Submersed leaves elongated and narrowly tapered, seemingly 

 »uninerved» but properly with three vascular bundles, floating leaves 5 — 7-nerved. 

 Upper peduncles about 10 mm long, above a little club-shaped. Stem lacking 

 subepidermal bast. 



Morong has distinguished tvvo varieties of this species (1. c. 48, 49) : — 

 multidenticulatus and tricJwphyllus. To those should be added a verv low-grown 

 (1 — 3 cm) terrestrial form with merely coriaceous or subcoriaceons, more or less ob- 

 tuse leaves and small two-flowered spikes with fruit of typical shape: 



f. limosus n. f. 



Statura humillima; folia omnia ± obtusa ± coriacea. 



This beautiful form is gathered »in the mud of Goose Pond, Dune Park, Ind., 

 U. S. A.» in 1898 by Rev. E. J. Hill, who has kindly sent me a specimen. 



Distribution. N. America, South Nattick, Mass., Morong (hb. Stockholm.), 

 Wellesly, Mass., 81, Morong (hb. Stockholm.), Andover, Mass., 80, Blake (hb. 

 Stockholm.), Nov. Ang]., Tuckerman (hb. Uppsal.), St. Louis, Mo., Geyer, 42 (hb. 

 Uppsal.), labelled »P. diversifolius Barton v. spicatus Engelman». It is not, known 

 to me that Engelman has published this name. Middle Florida, Bugel (hb. Stock- 

 holm.), Baltimore, Md., Taylor (hb. Stockholm.), Cuba, Wright, No. 3204 (hb. 

 Stockholm.). Mexico? S. America? 



Ser. B. Nuttalliani Hagstr. 

 P. Nuttallii Cham. & Schlecht. 



De plantis in exped. spec. Romanzoffiana observ., in Linnaea. 1827, 226. — 

 P. pensylvanicus Willd. ap. Cham. et Schl., 1. c, 227. — P. pumilus Wolfg. ap. 

 Schultes, Mantissa III, 1827, 354? 1 — P. Claytonii Tuckerman, Observ., in Amer. 

 Journ. Sci. and Arts, 1843, 38. P. epihydrus Raf. In Med. Rep. VI, 5, 1808, 



354? See the Index! — Fig. 62. 



This species is easily recognized by the fructification and by the floating leaves 

 having their apex rounded with a slight curve outward and their base sloping into 

 the stalk. Petiole of the length of the blade or shorter, the nethermost leaf often 



1 The statement of the width of the submersed leaves, »3—4 lin. lata» does not agree with P. Nuttallii, 

 rather with P. cayugensis (Wieg.), or with P. nodosus X Nuttallii, hence my hesitatation. 



