KUNGL. SV. VET. AKADBMIENS HANDLINGAE. BAND 55. N:0 5. 259 



P. bupleuroides Fern, x grainiiieiis L. (P. subiiiteiis n. hybr.). 



Some plants from the eastern states of N. America must be held for bupleu- 

 roides-hyhrids. They are like the 7iitens-iovms of Europe, but differ in habit and 

 leaf-denticulation. The latter is extremely inconsiderable. That is the case with a 

 ^ra?;imeMS-hybrid from Wenham Lake, Mass., 1882, leg. Faxon (hb. Stockholm.). 

 Anatomically this hybrid cannot be distinguished from P. nilens. — 



A hybrid form from the Mystic Pond, Mass., P. mysticus MoR., is by Fernald 

 (1. c. 75) held to be: 



P. bupleuroides Fern, x pusilliis L. (P. mysticus Morong in Bot. Gaz. 1880, 50). 



The anatomy of the stem does not contradict this supposition. Central cylin- 

 der thin, its crosscut-form suboblong, endodermis of 0-cells. No cortical strands, 

 but a few very thin subepidermal ones, resembling those of P. pusillus. Also other 

 characters point in the same direction especially the form and nervation of the leaf- 

 apex, the thin peduncle, and the short spike. — 



A plant from Lake Bantam at Ditchfield, Conn., coll. 25. VII, 83 by T. Mo- 

 rong (hb. Stockholm.) has weaker ligules than P. Richardsonii usually has, but 

 stronger than has P. perfoliatus. Leaves short, denticulation not quite typically 

 that of P. Richardsonii. It might be P. bupleuroides Fern. X P. Richardsonii (Benn.) 

 Rydb. American botanists, I hope, will consider the hybridism between perfoliatus, 

 bupletir., and Richardsonii. 



Sectio V. Laterales Hagstr. 



Enantiofhylli Koch, Synops, 1837, 678. — Oroenlandia Gay in Comptes rend. 

 Acad. sc. Paris, 1854, 703, pro gen. 



Caulis teres. Folia basi breviter vaginantia, serrulata, subopposita, floralia 

 stipulata. Stipidce laterales. — Prcefoliatio convoluta. Hybernacula desunt. 



The single species belonging hereto exhibits a peculiar habit and stipules strange 

 to all the other species, which have made J. Gay consider the plant a separate ge- 

 nus Groenlandia. We shall soon see that the fruit also presents properties deviating 

 considerably from what we have hitherto heard of the Potamogeton-irmt, and by 

 which P. densus occupies a position intermediate between Polamogeton on the one 

 side, and Zannichellia and Althenia on the other, as Ruppia forms a transition to 

 Dijilanthera. 



Although there are strong reasons for detaching P. densus from the genus 

 Potamogeton, and although I acknowledge that this section has another position 

 than the four preceding ones, and almost should be considered an appendix sooner 

 than a real section of the genus, I, however, follow the traditions of our great 



