KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. NIO 5. 67 



Ekerotii and others (hb. Stockholm., Uppsal, et Lund.); West-Gothia, Dinstorpsjön 

 in Sandhem, 87, Norstedt (hb. Uppsal, et Lund.), Vartofta, 92, Malmgren (hb. 

 Uppsal.); also in east Smoland according to S. Almquist; Scania, many places, col- 

 lected by Agardh, Thedenius and many others (hb. Stockholm., Uppsal, et Lund.). 

 Westward it is misreported from Ätran in Halland by E. Fries in his Flora Hallan- 

 dica. P. com/pressus Fl. Hall. = P. obtusifolius M. & K. (see under this species!). 



Norivay, Christiania, 45, Blytt (hb. Stockholm, et Uppsal.). — The scandina- 

 vian occurrence of P. zosterifolius, therefore, seems to coincide nearly with that of 

 P. crispus. The difference is that the former appears a little more towards the north 

 than the latter. The northern limit may be the year-isotherm of +3° or + 2° C. 

 — In Finland it is met with in Lakkola, 53, Viklander (hb. Uppsal.), in Karelia 

 austr., 80, Olsoni and others (hb. Stockholm, et Uppsal.), in Karelia oneg., 63, 

 Simmons (Jib. Uppsal.). 



Asia, south part of Baikal, 55, Rådde (hb. Stockholm.). Japan, Sorachi, 98, 

 Faurie. N. America, Canada (hb. Uppsal.). 



From this northern limit it seems to spread through the old and new world 

 to the year-isotherm of about + 12° C. In the Swedish Museums specimens occur 

 from the United States: Wisconsin (hb. Uppsal.), Minnesota (hb. Stockholm.), Michigan 

 (hb. Stockholm.), f. selenocarpus, and Massachusetts (hb. Stockholm.). — Europé, 

 from many stations in Denmarlc and Oermany (hb. Stockholm., Uppsal., Lund. et 

 Gothenb.); Belgium, Westerloo, 66, HiESENDONCK (hb. Lund.); Switzerland, Neuchåtel, 

 Lac d'Etaliéres, 69, Tripet (hb. Uppsal, et Lund.); Poland, Lithuania, 98, Dybow- 

 ski (hb. Stockholm.). 



P. acutifolius Link. 



In Roemer & Schultes, Systema vegetabilium, III, 1818, 513. — P. cuspi- 

 datus Schrader in Smith, Engl. Fl. I, 1824, 234. — Fig. 25, 26, 27. 



A noticeable peculiarity characterizes the genus Potamogeton in the manner 

 that nearly allied species of ten appear in pairs. This is the case with P. Robbinsii 

 and P. Maackianus treated of above. The same is to be stated of P. polygonifolius 

 and coloratus, P. gramimus and lucens, P. polygonus and Ulei. P. zosterijolius and 

 acutifolius also exhibit very great conformity with each other. Therefore some 

 authors consider the latter to be a variety of the former (thus already Schultes in 

 Mänt. III 1827), others look upon it as a subspecies or at least a dubious species. 

 However the fact may be explained, to me P. acutifolius nevertheless seems well to 

 defend its rank as a true species. This results both from a comparative examina- 

 tion of the two species and from the fact that the cross-breed is entirely sterile. As 

 to the fructification the difference at first glance is not very obvious. The ripe 

 fruit of P. acutifolius very seldom lacks the basal boss inside, which in P. zosterijo- 

 lius again is the normal condition. By this the fruit of the former generally ap- 

 pears broader than that of the latter (ef. Chamisso's description in Linnsea 1827!). 

 Both fruit-forms, however, occur in P. zosterifolius and even sometimes in the same 



