242 J. O. HAGSTRÖM, CRITICAL RESEEARCHES ON THE POTAMOGETOXS 



now more nodosus-\\ke. In the latter case the cortical bundles again are more niime- 

 rous, (2 — )3 circles, in the former fewer, 1 — 2 circles. 



For the rest this hybrid varies with more prominent serrulation (lucens-Mke), 

 wheras the leaves otherwise verge toward P. nodosus, or with weaker, nodosus-Vike 

 serrulation together with large leaves and short petioles (lucens-Mke), but with nodosus-like 

 apex. Thus especially the Danish form from Gudenå, whieh is >P. fluitans f. suh- 

 lucens Baagöe> in Asch. & Graebn., Synopsis 1897, 308. P. olivaceus Baagök. 

 Prép. des Hydroph. 1900. When I first was studying this plant (1899) I con- 

 sidered it to be the hybrid alpinus x lucens (hence the ad mission alp. x lucens 

 J. Baagöe, 1. c.), though some characters, especially the petioles of the sub- 

 mersed leaves were opposed. I thought me bound to this conclusion, because P. 

 nodosus does not occur in Denmark at present. When establislung the only 

 possible combination, lucens x nodosus, it is clear, that 1 also admit P. nodosus to 

 liave formerly belonged to the flora of Jutland, though probably by the disimpro- 

 vement of climate it has now disa})peared from it, just as, for instance, Trapa notans 

 from the southern Swedish waters. By its relationship to P. lucens the hybrid 

 is more adapted to a rough climate and has consequently been able to endure. 



The American examples are somewhat dissimilar among themselves: one spe- 

 cimen without floating leaves (more lucens-like) , the others eudowed with such leaves, 

 thus more nodosus-like, but all with longer petioles and more reduced lamina tliau 

 the Jutland specimens. Anatomically they behave alike. 



Under the name of P. Rugelii Ar. Bennett has distributed some Florida spe- 

 cimens as a hybrid P. americanus X lucens (The Journ. of Bot. 1908, 250, without 

 descr). Although I consider P. americanus to be P. nodosus, I do not, however, 

 use the name of P. Rugelii, because I suspect the Florida ])lant to be something 

 other than a lucens-hybrid. 



Distribution. Denmark, »In ämne Gudenå ad Kongensbro, Jyllandia», 99, 

 Baagöe (hb. Stockholm., Uppsal., Lund.). — N. America, i In lacu Seneoa ad Geneva, 

 N. Y. »84, Moronu (hb. Stochholm.), labelled: *P. lonchilcs». 



IV lucens L. x perfoliatns L. 



(P. decipiens Nolte in Hansen, Herb. der Schleswig— Holstcin— Lauenburgischc-u 

 Plor no. 715, 1838, et in KOCH, Synopsis Fl. germ. et helv., 1844, 779. — l\ lithua- 

 nicus Gorski, Herb., et in Reichcnb., Icones, VII, 1845, t. XXXI. — P. olivaceus 

 Lam; it. Flora 1846, 472.) 



On this beautiful hybrid the following observations may be made: 1) In the 

 description of Km n (1. c): foliia omnibus — — — basi rotundatis sessilibus ovali- 

 hus oblongisre ol)(usis mucronatis, margine laevibus, pedunculis Sdqualibus etc, the 

 last two oharacteristics are incorreotly given, in as muoh as the leaf margin ia some- 

 wliat rough by small, hut oltcu vciy soon decaying, or abraded teeth, most diatinotly 

 visihlo in verv young, not yel quite tull-grown leaves, and the peduncles oftcn or 





