KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. N:0 5. 201 



(lacunse along the principal nerves). Colour dark-green as most often in P. illinoensis. 

 Their tips obtuse and often with the broad shape characteristic to the last mentioned 

 species. To this shoidd be added that they are always petioled with sloping bases 

 quite in accordance with the above proposed species, in length intermediate or more 

 approaching to P. illinoensis (shorter petioles). 



Observing again that the plant is always endowed with floating leaves we 

 conclude that at least one of the parents but rather both produce such leaves. In 

 shape these leaves are intermediate but often smaller than in P. nodosus depending 

 on the fact that P. illinoensis presents a slighter ability of developing coriaceous 

 leaves than the coactive species. Those small floating leaves remind much of P. 

 NuUallii which fact seems to have been conclusive to Bennett (floating leaves are 

 nearly those of fensylvanicus : Benn.). Ligules, even the lower ones, persistent and, 

 besides, as to structure and length intermediate between P. nodosus and illinoensis. 



If we take the stem-anatomy as a starting point, all forms from Ferrisbergh 

 seen by me accord with each other. The central stele and the endodermis belong decid- 

 edly to P. illinoensis. The cortical bundles, again, are considerably reduced, evi- 

 dently an influence from P. nodosus, with weaker ligules and typically lacking cortical 

 strands. In the hybrid I have discovered a few interlacunar bundles but no 

 subepidermal strands. 



Thus we find that the morphological as well as the anatomical conditions of 

 the plant agree with each other and unanimously argue for my proposition above; 

 and as the plant, moreover, belongs to the distribution-area of those species, sufficient 

 evidence may have been presented for its correctness. 



The specimens from the Lake Champlain ad Ferrisbergh are preserved in the 

 Nat. Hist. Museum at Stockholm. — On the hybrid P. Zizii from the same locality, 

 vide p. 216. — The hj^brid P. alfinusxNutkdlii (pensylv.) is as yet not discovered. 



p. illinoensis Mor. x perfoliatus L. (P. subdentatus n. hybr.) 



Caulis ramosus ramis angulate curvatis in modo P. perfoliati. Anatomia ut 

 in P. illin., vide fig. 99, CI Folia caulina inferiora sessilia, elongata, debiliter dentata; 

 nervatura et apices ut in P. illin., basi lanceolata v. subovata. Ligidm fuscse ut in 

 illinoensi sed breves, caducseque (P. perfol.). 



Two forms are found : 



a. sessilis: — Fol. floralia sessilia. — Collected in N. America, Queenston, Ont. 

 (lib. Haun.). 



P petiolatus: — Fol. floralia petiolata. — Coll. in Griffin Lake, B. C, N. Amer., 

 89, Macoun (hb. Haun.). 



P. subdentatus differs from P. nitens through the nervation, the leaf-apex, narrower 

 leaf-base, and the colour of the sheaths. 



K. 8v. Tet. Akad. Handl. Band 55. N:o 5. 26 



