238 — 



The other lake H ars j ön belongs to the alpine region and is 

 about 650 m. above sea-level. The higher vegetation is very poor, 

 only in shallow bays, more or less separated from the lake proper, 

 a few Spargania and Potamogeton alpinus occur. The plankton 

 was collected here, as in Lomnæssjon, by dragging a funnel-shaped 

 net of miller's gauze Nr. 20 behind a boat slowly rowed. The 

 temperature of the surface-water was on the 18 th of July 1900 

 14° C. Here also the main part of the plankton consists of animals, 

 viz. copepods and daphnids, e. g. the strange Rolopedium gibberum 

 was common. The phytoplankton was however rather rich; Sphœro- 

 cystis, Botryococcus, Stichogloea and Coelosphœrium Nœgelianum are 

 the predominant forms, but other Ghlorophyceœ and Myxophyceœ 

 occur. The phytoplankton is very different from that of Lomnæs- 

 sjon and of the Lappland lakes which Miss Cleve has investigated. 

 On the other hand, the resemblance to the phytoplankton of the 

 lakes in Switzerland is very striking. Professor Chodat 1 ) has just 

 described the two genera Sphœrocystis and Stichogloea from the 

 Swiss lakes. Also the lakes in Finland 2 ) contain a phytoplankton 

 which in many points come near the phytoplankton of Harsjön, 

 they have more particularly the frequent occurrence of Coelosphœ- 

 rium in common ; but the phytoplankton of the latter differs in 

 having diatoms in great abundance while they are very rare in 

 Harsjön — at least in the summer; e. g. Asterionella formosa is 

 quite absent. 



The entire absence of Peridiniaceae in Harsjön is also an 

 interesting fact and one which it has in common with the plankton 

 of Lomnæssjon. 



The plankton of the Norwegian lakes is not well-known, only 

 some publications of Professor Wille 3 ), H. Huitfeldt-Kaas 4 ) 



1 ) Chodat, R. : Études de Biologie lacustre. Bull, de THerbier Boissier 1897. 



2 ) Le va nder, K. M.: Zur Kenntniss der Fauna und Flora Finnischer Binnen- 

 seen. — Acta Soc. pro Fauna et Flora Fennica XIX, % 1900. 



3 ) Wille, N. : in Biologisches Centralblatt XVIII, 1898, Nr. 8. 



.— Algologische Notizen I— VI, Nyt Magaz. f. Naturvidenskab 38, 1900; 

 VII- VIII, Ibidem, 39, 1901. 



4 ) Huitfeldt-Kaas, H. : Plankton in norwegischen Binnenseen. Biologisches 

 Centralblatt XVIII, 1898. 



— Die limnetischen Peridineen in norwegischen Binnenseen. Kristiania, 

 Vidensk Selsk. Skrifter 1900, Nr. 2. 



