220 J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



spathulalus M. & K.»; Umenau, 86, C. Nöldeke (hb. Breman.); Berlin, Potsdam, 

 Havel bei Baumgartenbriick, 83, Scheppig (hb. Brem.); more dubious forms are seen 

 from Schlesien (Silesia), Vratislavia, 64, Uechtritz (hb. Stockholm.), and Nassau, 

 83, Tiselius (hb. Stockholm.). — England, Surrey, 86, Bennett (hb. Stockholm.); 

 Yorksliire, River Ure near Ripon, 80, Niciiolson (hb. Lund.), labelled: P. polygoni- 

 folius Pourr; Shobden March, Herefordshire, 89, Rev:d A. Ley (hb. Ar. Bennett). 

 - Ireland, Lough Corrib, Galway, 53, Kirk (hb. Uppsal.): »P. Kirkii Syme»; Maam 

 Co. Galway, 85, Linton (hb. Stockholm.). — Scotland, a dubious form from Caithness, 

 86, Marshall (hb. Stockholm.). — A couple of rather dubious plants from Faroe 

 Islands are present in hb. Stockholm. 



North America. Pine Plains, New York, Hoysradt (hb. Stockholm.), by 

 Morong labelled: P. Oakesianus Robbins. The relationship with P. gramincus and 

 natans seems rather obvious. 



P. grnmineus L. x nodosus Pom. 



(P. argutulus Hagström, New Potamogetons in Bot. Not., 1908, 106—108. 



Cfr. Eug. Simon, Une pl. poitevine nouv. pour la se. in Hull. Soc. 

 Bot. des Deux-Sévres 1913—14, 37—44.) — Fig. 105. 



Two froms of this hybrid are present in the Museum at Upsala 

 both of them originating from New England and belonging to the no- 

 dosifolius series of the hybrid, but otherwise a little deviating one 

 from the other. 



All forms of this hybrid have scrrulate snbmersed leaves a little 

 more durable than those of /'. nodosus, and ligules a little longer and 

 Fi R . los. p.argu- more deciduous than those of P. gr aminens. The latter species mostly 

 dosifnnll-u^ni"!, predominates in the stem strueture. 



Top of a subm. leaf 



of the Tnokennan a gramineifoliUS BaQSTR. 1. C. 



plant, J. II, Top of ° ... 



a subm. leaf of the (Jauhs ramosus; jolia ramea lanceolata sessilia. 



Morongian punt. Thifl var {a ^escribed and figured in t lic aforecited papers. 



p nodosifolius Hagstr. 1. c. 



Caulis simplex v. subsimplex; jolia i. pctiolata. 



The Tuckerman specimen (sec below) has long internodes; Biibmeraed Leaves 

 long-pctioled (2—6 cm.) acutc; floating leaves rather nanow, Long-petioled; ligules 

 long, 5-7 cm, with ridges similar to those of /\ nodosus, rather durable like (lie 

 lower leaves (/'. gramineua). Habit like /'. nodosus. WhoUy sterile. Anatomy of 

 stem ncarly (jnite as /'. gramineua exoept bhat the central cylinder has two median 

 xylem-eanals and ueaker w-cells in the endoderniis (inlhienee Ironi /'. nodosus). 



The other plant collcetcd by T. AfoKONG is a barren shoot without floating 

 leaves, in habit more like /\ gramincus with shorter stem-leaves and Bhortet petiolcs 

 (1 — 3 cm). Leaves semilate, a little obtuser than in the forogoing, in size 6—10 X 



