KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55- N:0 5. 211 



continued quite up to the present, is the most evident proof of the impossibility 

 to keep up the difference between a separate species standing between P. gramineus 

 and lucens, and the hybrid of both. 



For the sake of completeness I will here communicate a review of the opinions 

 held by the modern authors. If we begin with S. Almquist, his view is given in 

 Hartman's Handb. Skand. Flora (Krok ed.) 1889, 47. Part of the intermediate 

 forms between lucens and gramineus may be hybrids; another part are imitative 

 forms, which, until further, he summarizes under the name of P. lucens [3 Zizii. He 

 was the first to suggest the hybridity of certain Zizii-iorms but gives the name 

 Zizii to some imitative forms (»härmformer») that is to say forms imitating or 

 approaching to P. gramineus. Keeping up in the same direction A. Fryer, On the 

 specific rank of P. Zizii, in The Journ. of Botany, 1892, 114 — 115, regards the typical 

 forms of P. Zizii as more or less fertile hybrids between P. lucens and P. gramineus 

 L. In the varying fruiting ability especially he finds a »character which strongly 

 points to hybridity». T. Morong again in his aforesaid Revision of the North 

 American Najadaceae, 1893, 29, classes P. Zizii, under the name of P. angustifolius 

 Berch. & Presl (fide Ar. Bennett), as an independent species, but with the remark: 

 »seems to be intermediate between P. heter ophyllus and P. lucens.» G. Tiselius in- 

 cluded P. Zizii with the varieties of P. lucens which he displayed in his Potamoge- 

 tones suecici exsicctati, fasc. II, 1895 nos. 59 — 65. He considered those forms to 

 be more primeval than the proper P. lucens: Verisimilius esse videtur, has om nes 

 formas minores esse vetustiores vel primarias, atque causis ex multis suspicor, P. 

 lucentem »verum», formam robustiorem, quse in rebus opportunioribus crescit, paula- 

 tim ex iis minoribus exstitisse formis, quse nunc plerumque in rebus angustioribus 

 et nasci et vivere videntur (Notula 59). Thus the quite reverse to what all 

 reasons claim. L. Vuijck renews the earlier supposition of P. Zizii as a variety of 

 P. gramineus L., in Nederl. Kruidk. Archief, 1895, 653. C. Raunkijer mentions it 

 again as a variety of P. lucens in De Danske Blomsterpl. Naturhistorie, 1896, 59. 

 O. Hagström in Neuman, Sveriges Flora, 1901, 796, does not know any intermediate 

 species between P. gramineus and lucens; all the intermediate forms are of a hybrid 

 origin. Influenced by this Swedish author J. Baagöe says of the forms concerned, 

 »perhaps a hybrid» (Potamogetonacese from Asia-media in Vidensk. Meddel. 1903, 180). 

 From the same source K. R. Kupffer may also have been induced to speak of the 

 hybrid gramineus X lucens as identical with P. Zizii, in Von zur Muhlen, Die Potamoge- 

 tonen des Ostbaltikums, Riga Korrbl., 1906, 168. Ar. Bennett does not admit this 

 hybrid in Linton's List of Hybrids in The Journal of Botany 1907, 299, but speaks 

 further on (p. 373) of P. angustifolius Bercht. & Presl, which he considers to be 

 the correct name of P. Zizii. That is, however, not at al] quite certain. On the 

 contrary it is most likely that P. angustifolius as well as P. paucifolius, both originally 

 gathered by Opiz in ponds at Bohdanec, where also P. heterophyllus (= P. gramineus 

 L. with floating leaves) was growing, are only gramineus-iorms without floating 

 leaves. And the very description, published by Bennett in The Journ. Bot., 1889, 

 263, suggests the same, especially the expression folia stipulis angustiora. A Zizii-iorm 



