98 J. A. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



species. Leaves with stronger nerves than in pusillus but with at least one chan- 

 nel-row along the mid-rib. Apex usually mucronatus-like. Ligules commonly a little 

 longer and more persistent than in P. fusillus. It is infallibly recognized by the 

 turios, when present, since something of P. mucroyiutus is always to be found in 

 them. The specimen from Norby (hb. Uppsal.) is provided with fruit, which is a 

 little larger than in the common pusillus. The fruit of P. Berchtoldi is also said to 

 be larger than in P. pusillus. I think it impossible now to state whether all that 

 FiEBEE, referred to his new species may be this hybrid, or if not partly pure P. pu- 

 sillus, partly also the hybrid P. dualis m. is comprehended in it. The latter is very 

 likely to be the fact, and when the name Berchtoldi is already applied by Ascherson 

 and Gkaebner (Synopsis) to a true pusillus-iovm, we shall have to give new names 

 to the hybrids included in P. Berchtoldi of Fieber. 



Distribution. Siveden, Uppland, Uppsala, Norbj^ in the river, 51, Zdt (hb. 

 Uppsal.); Sigtuna, in a clay-pit at the bridge leading to Garns-bay, 82, Floderus 

 et TisELius (hb. Stockholm.). — Scania, Bjorka in the parish of Kropp, 64, Htjlt- 

 BERG (lib. Lund.) — Besides P. pusilliformis occurs in Denmark, where it is collected 

 by Baagoe in Skjerna between Clasensborg and Felding in Jutland in 1902, and 

 in Skaber Molleso (mill-lake), Jutland in 1905. — Specimens from Gull Lake, Cass. 

 Co., Minn., U. S. A. 93, Ballard (hb. Stockholm.) also seem to me to belong to 

 P. pusillijortnis. 



P. paiioi'initaiiiis Bivona Bernardi. 



Nuove piante inedite del barone Ant. Bivona Bernard: pubblicate dal figlio 

 Andrea. Palermo, 1838, 6—7. —P. gracilis Fries, Novitise Fl. Suec, 1828, 50. — 

 P. Noliei Bennett, The nomenclature of Potamog., in The Journ. of Bot. 1890, 300. 

 — Figs. 38, 39. 



The earliest trace we find in the literature of this species is in the monograph 

 of the genus by Chamisso and Schlechtendal in 1827. For, if certainly the nar- 

 row-leaved form of panormitanus is not alone included in their P. pusilhis L., D. 

 forma tenuissima, the description, nevertheless, is made so as to comprehend it 

 therein, since the leaves are said to be »S8epe convoluta et inde subsetacea» etc. 

 This narrow-leaved form, properly P. pan. p minor Biv. is in the next following 

 year discerned by E. Fries under the name of P. gracilis, the specific character of 

 which he still in 1846 (Summa veget.) insists upon chiefl}' on account of the prominent 

 midrib of the leaf and the lack of lateral nerves, though he had found it only in 

 one single localitj^ (in stagnis marinis ad Landskrona). Hartman adopted and main- 

 tained the species in the different editions of his Handb. i Skand. Flora, but only 

 bowing to the eminent authority of Fries and with a certain reservation. In the 

 year 1838 the same species suddenly appears in the above named treatise by Bivona, 

 but now not only in its thinnest but mainly in its most broad-leaved form. Also 

 Bivona bases its specific rank principally on the stiff leaves, to which he adds the 



