It was in the year 1891 that I commenced studying the aquatic plants. At 

 first indulging in the small Gallitriches, I låter took to the greater and by far more 

 interesting genus Potamogeton. Concurrently with the most necessary observations 

 in nature I was favoured with having access to the considerable collections of the 

 late Dr. G. Tiselius and the also deceased chemist J. Baagöe. By the kindness 

 of the 1 ätter I succeeded in getting into correspondence with several foreign botanical 

 institutions. For the access to the Swedish museums I am greatly indebted to the 

 favour of their benevolent directors and assistants who, moreover, have most kindly 

 rendered accessible to me all desirable literature. And at the Bot. Museums of the 

 universities of Christiania and Copenhagen I have met with the same benevolence 

 and complaisance, for which all I herewith am saying my best thanks. I am espe- 

 cially under great obligation to Prof., Ph. D. C. Lindman, Stockholm. Without his 

 powerful assistance and instructive advice the present work had scarcely been pub- 

 lished. 



To my appreciated friends, Director Fr. Fant, at Hall, and Barrister B. Lager- 

 wall, at Drottningholm, as well as to Ph. D. F. Kempe, of Stockholm, and Ph. D. 

 I, Lagerwall and Mrs. I. Lagerwall, of Stockholm, I herewith offer my sincerest 

 thanks for their encouragement and the valuable aid they have rendered to me. 



Lastly I render my most respectful thanks to Miss Hedvig Svensson, of Stock- 

 holm, who has kindly assisted with the time-wasting proofreading. 



The Swedish museums contain important collections of Potamogetons. Thus 

 an abundant material is deposited in the Natural History Museum at Stockholm 

 (Riksmusei Botaniska Afdelning). It possesses collections that have belonged to 

 P. Beurling, P. A. Boren, R. F. Fristedt, Joh. Lange, L. L. L^stadius, E. F. 

 Nolte, C. F. Nyman, C. M. Nyman, H. F. G. Strömfelt, K. Fr. Thedenius, G. 

 Tiselius, J. Ångström, and many others. In Upsala there are a great many interest- 

 ing forms from the herbaria of M. M. Floderus, Elias Fries, T. M. Fries, C. J. 

 Hartman, R. Hartman, L. L. L^estadius, C. O. Schlyter, E. Tuckerman, P. J. 

 Zetterstedt and G. Wahlenberg, among others. The Botanical Institution of the 

 University of Lund has collections brought together by J. G. Agardh, M. von Du- 

 ben, F. Elmqvist etc. In the museum of Gothenburg we find the herbaria of 



