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



of some small-leaved form of P. illinoensis by their slight size. Besides, the sterility 

 also suggests the hybrid origin of this plant. 



P. fseudolucens occurs »in lacu Fresh, Cambridge, Mass., U. S. A.» gathered 

 by T. MoRONG, 1880 (hb. Stockholm), and at N. Haven, Ct., 1858, Eaton (hb. Christ.). 



Of P. 'pseudo-Zizii, m., which is P. gram.in. X illin. x lucens, see under P. 

 gramineusf 



P. illinoensis Mor. x nodosus Poir. (P. Faxoni Morong, A revision of the North 

 American NajadacefE etc. in Mem. Torr. bot. Club, III, 2, 1893, 22, t. XXXII). — 



The Potamogetons gathered by C. E. Faxon in the years 1880 and 1882 at 

 Ferrisbergh, Vermont, U. S. A., have been judged of very differently. Faxon himself 

 seems to have held them for P. rufescens (= alpinus). Ar. Bennett has thought 

 them to be P. rufescens y. Nuttallii (Claytonii) (i. e. : alpinus X NuUaUii) (Journ. of Bot., 

 1890). In 1893. T. Morong has described them under the name of P. Faxoni and 

 also thought them a hybrid, but proposes the combination lonchitis X rufescens (i. e. 

 alpinus X nodosus). In Britton & Brown, 111. Fl., 1896, this suggestion is not 

 further mentioned, in consequence whereof it is probable that Morong before his 

 death has abandoned it as too uncertain. In 1901 Ar. Bennett (Journ. Bot.) seems 

 to have been inclined to leave the thought that P. alpinus has been a co-agent. 

 Any closer explanation, however, is not given. P. Graebner establishes P. Faxoni 

 (1907) as a proper species of the '>subseciio Alpini-*, but refers also to the opinion 

 of Mr Ar. Bennett (1890) though with some hesitation (»?»)• Finally Mr Ar. 

 Bennett has in The Journ. of Botany, 1908, 248, on account of the habitats, as- 

 serted quite a new idea of two different hybrids: one which he names P. americanus 

 {lonchites) Quam. X pensylvanicus Cham., originating from » Little Otter Creek », and 

 the other from »Lake Champlain», which he calls P. alpinus X pcnsylvanicus or x P. 

 Champlainii. Bennett is of the opinion that the former of those ought to main- 

 tain the name P. Faxoni. 



Before we enter upon an investigation of the plants concerned, I should state 

 first that I have had an opportunity to study specimens of both the stations collect- 

 ed by Faxon himself and belonging to Morong's herbarium and by him determined 

 as P. Faxoni; and further that the Little Otter Creek is one of the rivulets flowing 

 into the Lake Champlain (emptying into the lake: Mor.). 



An examination of the fructification plainly shows that it is about a cross- 

 breed. The difficulty is to find the two parent species of the hybrid. 



If you examine the submersed leaves you will find that both the forms are 

 characterized by the margin not being smooth as in P. alpinus and Nuttallii, but 

 studded with small faint teeth. From that fact the sure conclusion can be drawn 

 that at least the one of the parents but rather both the partaking species must be 

 endowed with serrulate submersed leaves. Consequently the combination alpinus X 

 Nuttallii is inconceivable. The submersed leaves are further characterized by a nerva- 

 tion and structure typical of P. nodos^is and in some degree also of P. illinoensis 



