210 J. O. HAGSTRÖM, CRIT1CAL RESEARCHES OX THE POTAMOGETOXS. 



This hybrid is recognizable by the leaves of the spike region (floating and 

 transitional leaves), which are ronndly obtuse with broad obtuse mncro and their 

 petioles are often shorter than the lamina. In Zucens-hybrids the apexes of those 

 leaves usually are narrower and sharper. Submersed leaves lanceolate, serrnlate, 

 dark-green, short-petioled or with a stalk-like base, and cuspidate apex. The innermost 

 sidenerve runs nearer the midrib than in the hybrid P. Zizii, which usnally reminds 

 more of P. lucens. Ligules strong, persistent, and in general longer than in P. 

 gramineus. As in the morphology so it is also in the stem anatomy intermediate 

 between the parent species. Interlacunar cortical strands occur in one circle, which, 

 however, contains more bundles than has P. gramineus (influence from P. illin.). Some 

 subepidermal strand or other as in the parents. Endodermis of strong M-cells, 

 and central stele usually with two median xylem-canals as in P. illinoensis. Lateral 

 bundles now as in P. gramineus, now free as in P. illinoensis. By the anatomy this 

 hybrid can hardly be distinguished from P. illinoensis X lucens, which again is distin- 

 guishable by its more lucens-Wke leaves and the lack of floating leaves. Also P. 

 gram i neus X lucens (P. Zizii) has a more or less lucens-likc nervation especially in 

 the branch-leaves. Beside the more elongate leaf-apex, the last mentioned hybrid 

 typically has only one median xylem-canal in the central stele of the stem and fused 

 lateral bundles. 



Distribution. N. America, In lacu Pleasant ad Wenham, Mass., U. S. A., 

 Morong (hb. Stockholm.), labelled: »Potainogeton Zi-.ii M. K.»; Green Lake, Chicago 

 Co., Minn. U. S. A., 92, Taylor (hb. Stockholm.); Canada, station and collector 

 not named (hb. Stockholm.) bears a couple of gramineus-hke fruits. The »P. spathula- 

 formis (Rob b) Mor., P. varians Mor.» (hb. Stockholm., Uppsal.), gathered by T. 

 .Morong in Mystic Pond at Boston, seems to me to belong hereto. At all eventa 

 it is a real gramineus hybrid. The stem anatomy argues rather for a combination 

 with illinoensis than with lucens. The apexes of the floating leaves do not contradict 

 this suggestion. - A plant from Glenwood, Minn., 91, Taylor (hb. Haun.) is likely 

 to be P. gramin. x illin. X lucens (P. pseudo-Zizii n. hybr.): Folia subm. sossilia v. 

 subsessilia. 



I*, gramineus L. x lucens L. 



(P. Zizii Mebt. et Koch, Deutschlands Flora I, 182.'}, 845. — P. lurens p nitens 

 Cham., Ådnot. 1815, 6. — P. lucens p rotundifolius Sohultz, Flora starg. BuppL 1, 

 1819, ( .». /'. lucens v. augusti folius Geay, Nat. arrang. Brit. Pl. 1821, ;>4. — P. 



angu8tifoliue Pbesl, Rostlinar aneb o prho/.enosti rostlin 1, 1821, 19? — /'. lulrro- 

 phyllus o lati folius Mkrt. et KOOH I. C. P. lurats a ovdlifolius MEBT. el Kocii I. c. 



849, j>. p. — /'. heterophyllus p fluviatilis Sohlecht., Fl. Berol. 182:5, 116? /'. 

 Proteus Zizii Cham. et Sohl., Linna?a, II, 2, 1827, 1!»7.) Fig. 103. 



The above w ritten list of synonynis till and including the year 1827 shows 



hou this hybrid has been conoeived: now as a proper Bpecies, now as a variety of P, 

 lucens or of gramineus, now as a variety of a new-established speoies P. Proteus &o.å 

 of similar value with /'. Inans and gramineus. This doubtfulnesa of the authors, 



