94 J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



Uppsal., Lund., Gothenb.), Nartuna in Trehorningen, 95, Wedberg & Tiselius (hb. 

 Stockholm., Uppsal., Lund.). — Jemtland, Hammerdal, Viken, 83, Jonsson (hb. Lund.), 

 northern-most station, year-is. + 2° C, Hassjo, Juleby (hb. Stockholm.). 



Denmark, Bornholm, 68, Nielsen and others (hb. Stockholm., Uppsal., Lund., 

 Gothenb.). — ■ Finland, Karelia oneg., 63, Simming (hb. Uppsal.). — Germany, Usedom, 

 54, Marsson; Kiel, Nolte (hb. Stockholm., Uppsal.). Bavaria, prope Altneuhaus, 05, 

 Fischer (hb. Stockholm), prope Adelsdorf, 05, Fischer (hb. Stockholm.), 49° N. L. — 

 Russia, In lacubus prope Vilnam, hb. Besser (hb. Stockholm.). • — Asia Pamir: Jashilkul, 

 98, Paulsen (hb. Haun.). — N. America, Nipigon, Lake Superior, 84, Macotjn (hb. 

 Stockholm.). 



P. riitilus WoLEG. X Vaseyi Robb. (P. gemmipariis (Robb.) Morong in Bot. 



Gazette, LS80, 51). 



Some specimens from » Eastern Mass., U. S. A., Coll. Th. Morong », now in 

 Uppsala museum, undoubtedly are the above written hybrid. Hitherto they have 

 been considered to be a distinct species and are as such figured in Morong, Naja- 

 dacese, 1893, t. LIV. They present so great resemblances to P. Vaseyi to the form 

 and structure of the leaves as well as to the turios that they necessarily must stand 

 in close affinity to this species (fig. 59). Other properties as for instance the size and 

 the longer outer leaves of the turios, the length of the peduncle, the ligules, stem- 

 sclerenchyma etc. denote P. rutilus. The sterility and sporadic occurrence indicate 

 also a hybrid origin and I am waiting no serious objection to my supposition of 

 P. rutilus X Vaseyi. 



P. miicronjitiis Schrader, ap. 



Reichenbach, Icones fl. Germ, et Helv. VII, 1845, 15. — P. pusillus var. 

 interruptus Schtjltes, Oesterr. Fl. 1814, 328. — P. compressus p tenuis Wahlenb., 

 Fl. upsal. 1820, 60. — P. compressus P elongatus Wahlenb., FJ. suec. 1824, 107. — 

 P. compressus (3 acutus Schlecht., Fl. berolin. 1823, 117. — P. pusillus v. A. Cham. 

 et Schl., Linnsea II, 1827, 171. — P. pusillus a. major Fries, Nov. Fl. suec. 1828, 

 48, — P. Friesii Rupreght in Beitrage zur Pflanzenkunde d. russ. Reiches 1845, 43. 

 — P. Oederi Meyer, Fl. hannov. excurs. 1849, 536. — P. major Morong, Najadacese 

 1893, 41. - Fig. 37. 



In habit this species is very much like P. panormitanus by the scarce occur- 

 rence of branches for the prolongation of stem according to the water-level. Usually 

 there is a spike-bearing branch in the axil of the upper involucral leaf and this 

 branch often stretches its internodes. This branch rarely bears a branchlet, and bran- 

 ches of the third rank might not at all grow out. The plant rather stretches the 

 topmost internode thus following an eventual rising of the water. From the leaf- 



