KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. N:0 5. 221 



1 — 1,5 cm, durable. Stem-anatomy more intermediate i. e. with fewer bundles than 

 in P. gramineus. 



I defer naming these forms till more material can be had. Meanwhile the 

 plants may be named the Tuckerman specimen and the Morongian specimen. 



Habitat. N. America, »Nov. Angl. », E. Tuckerman Jr. (hb. Uppsal.); New 

 England, T. Morong (hb. Uppsal.). — A specimen from » Jamaica, Swartz» (hb. 

 Stockholm.) might also belong to this hybrid, but is more dubious. It has narrowly 

 lanceolate leaves on petioles of 15 — 20 mm in length; stem simple, but only a barren 

 shoot without floating leaves is at hand. 



P. graiiiiiieus L. x perfoliatus L. 



P. nitens Weber, Supplementum fl. Holsaticse 1787, 5. — P. curvifolius Hartm., 

 Handb. i Skand. Flora, 1820, 78—79. — P. heteropJiyllus |3 lacustris Cham., Adnot. 

 1815, 5. — P. (Proteus?) curvifolius Hn, ex Cham. & Schl., Linnsea, 1827, 197. — 

 P. salicifolius Wolfgang in Schultbs, Mantissa III, 1827, 355. — P. divaricatus 

 WoLFG., 1. c? — P. falcatus Fryer in The Journ. of Botany, 1889, 65, t. 286. — 

 P. salignus Fryer in The Victoria County Hist. Devonsh. I, 1906, 129, Pot. Brit. 

 Isles, 1912, 76, pi. 49. — Figg. 106, 107, 108. 



In the course of time this plain hybrid has been conceived differently by differ- 

 ent authors and the opinions are still parted, as French, Dutch, and German resear- 

 chers continue to give a more independent position to a P. nitens (as species, or as 

 variety, or subspecies, and of like value with P. gramineus L. under a collective 

 species P. heterophyllus or gramineus), separate from a possibly existing hybrid 

 gramineus X perfol., of which the authors now concerned speak very reservedly and 

 vaguely. — Dr. G. Tiselius's view is in his herbal work expressed thus: Forma? multse 

 ad sirailitudinem P. graminei proximo accedere mihi videntur, nonnuUse sunt fortasse 

 P. gramineus X perfoliatus, alise P. gramineus X prcelongus, aliae dupliciter hybridse in 

 infinitum. 



No one has as yet been able to draw up any morphologic or other boundary 

 difference between the osjoecies" (subspecies) nitens and the hybrid. The main differ- 

 ence is said to lie in the fruiting faculty, which is supposed to exist in the former 

 but to be lacking in the latter. The fact is, though, that the greatest part by far 

 of all specimens belonging hereto show partly complete sterility partly a much 

 reduced fruiting ability. And when the fruit production is as it seems normal a 

 great percentage of the fruits will be found to be more or less defectively developed. 

 The same result we arrive at when examining the pollen. The least part of the 

 specimens possess a greater percentage of fertile pollen and these grains are often 

 of different size among themselves, in part being like those of P. perfoliatus (com- 

 paratively large), and in another part those of P. gramineus (smaller and slightly 

 ovoid). These facts beside the rich variation of the form of all organs, between 

 perfoliatus and gramineus, with both of which P. nitens also associates, make me quite 



