220 



J. O. HAGSTEOM, CRITICAL RESEABCHES ON THE POTAMOGETONS. 



spathulatus M. & K.»; Umenaii, 86, C. Noldeke (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.); 

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

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

 — Ireland, Lough Corrib, Gahvay, 53, Kirk (hb. Uppsal.): »P. Kirkii Sym^»; 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. OaJcesianus Robbins. The relationship with P. gramineus and 

 nalans seems rather obvious. 



P. gr.ainiiieiis L. x iiodosiis Pom. 



(P. argutidus Hagstrom, New Potamogetons in Bot. Not., 1908, 106—108. — 

 Cfr. EuG. Simon, Une pi. poitevine nouv. pour la sc. in Bull. Soc. 

 Bot. des Deux-Sevres 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 serrulate submersed leaves a little 

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

 Fig. 105. p. argil- moTo deciduous than those of P. gramineus. The latter species mostly 



tuhis Hagstii. S no- j • i • j.i j. j. j. 



dosifoiius hagstr. a, predominates in the stem structure. 



Top of a subm. leaf 



of the Tuckerman a graminelfolius Hagstr. I. C. 



a snb'm. leaf of the CwuUs ramosus ; foUa raiuca lanceolata sessilia. 



orongian plant. This var. is described and figured in the aforecited papers. 



p nodosifolius Hagstr. I. c. 



Gaulis simplex v. subsimplex; folia ± petiolata. 



The Tuckerman specimen (see below) has long internodes; submersed leaves 

 Ibng-petioled (2—6 cm.) acute; floating leaves rather narrow, long-petioled; ligules 

 long, 5—7 cm, with ridges similar to those of P. nodosus, rather durable like the 

 lower leaves {P. gramineus). Habit like P. nodosus. Wholly sterile. Anatomy of 

 stem nearly quite as P. gramineus except that the central cylinder has two median 

 xylem-canals and weaker i(-cells in the endodermis (influence from P. nodosus). 



The other plant collected by T. Morong is a barren shoot without floating 

 leaves, in habit more like P. gramineus with shorter stem-leaves and shorter petioles 

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



