210 J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



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

 transitional leaves), which are roundly obtuse with broad obtuse mucro and their 

 petioles are often shorter than the lamina. In liicens -hyhvids the apexes of those 

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

 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 usually reminds 

 more of P. hocens. 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 w-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 hicens-l\ke leaves and the lack of floating leaves. Also P. 

 gramineus X lucens [P. Zizii) has a more or less lucens-like 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. 



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

 MoRONG (hb. Stockholm.), labelled: >^Potamogeto7i Zizii 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-like fruits. The »P. spathulce- 

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

 MoRONG in Mystic Pond at Boston, seems to me to belong hereto. At all events 

 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. fseuclo-Zizii n. hybr.): Folia subm. sessilia v. 

 subsessilia. 



P. graiiiineiis L. x lucens L. 



(P. Zizii Mert. et Koch, Deutschlands Flora I, 1823, 845. — P. lucens p nitens 

 Cham., Adnot. 1815, 6. — P. lucens p rolundif alius Schultz, Flora starg. suppl. T, 

 1819, 9. — P. lucens v. angustifolius Gray, Nat. arrang. Brit. PI. 1821, 34. — P. 

 angustifolius Presl, Rostlinar aneb o prirozenosti rostlin 1, 1821, 19? — P. Jieiero- 

 phyllus latifolius Mert. et Koch 1. c. — P. lucens a ovalifolius Mert. et Koch 1. c., 

 849, p. p. — P. he.tero'pliyllus p jluviatilis Schlecht., F1. Berol. 1823, 116? — P. 

 Proteus Zizii Cham, et Schl., Linnsea, II, 2, 1827, 197.) — Fig. 103. 



The above written list of synonyms till and including the year 1827 shows 

 how this hybrid has been conceived: now as a proper species, now as a variety of P. 

 lucens or of gramineus, now as a variety of a new-established species P. Proteus and 

 of similar value with P. lucens and gramineus. This doubtfulness of the authors. 



