igSI. No. 4. THE PHVTOPLAXKTOX OF SOME NORWECaAX LAKES. 3 



surroundings are to the greater extent forests, but there are also impoi'tant 

 cultivated areas. Minne, where the sample was taken is situated in the South 

 of the lake near its outlet. 



The collection (from the surface Jtily 2. rS(j6.) contained such quanti- 

 ties of Astcrioiiclla gracilliiiia as to be prevalent in the phytoplankton, but 

 Ceratiiiiii Iiiniiidiiiclla and Mclosira graiiulata were also present in consider- 

 able quantities. 



3. Sog- n s vandet is a small lake in the immediate neighbourhood 

 of Christiania. The drainage-area is almost exclusively forest, and the water 

 without doubt ver\' little contaminated. It is situated at an altitude of 182 m's. 

 The whole lake is shallow, the maximum depth being only 15 m's. 



Five samples were examined. 



/. June 27. iSg6. The surface. \'erv rich phytoplankton. Aiiaùœi/a 

 flos-aquœ predominating with considerable quantities of Ceratiuni hirundiiiella 

 and scattered specimens of Art/irodesiuus Iiicits. The Protozoan Lithocolla 

 Apsteiiiii was common. 



2. June 2 J. i8(.j6. ]\iiical 11 lu^s. This vertical sample was a little 

 different from the horizontal, as it contained greater quantities of Artliro- 

 desnuis Incus. 



J. October ji. i<Sc)6. Surface. The phytoplankton was of no con- 

 siderable volume, Auaha'iui Leuuuerinauuii and Aiiabaiia flos-aquœ the only 

 Algae that occurred in any quantity. 



4. October ji. iSg6. J^ertiea/ 1 1 m's. — This sample differed from 

 the horizontal as Peridiniuui IJlllei was quite common, and Dinobryon ser- 

 tularia occurred in scattered specimens. — One must always remember that 

 b\- no means all Algæ in the plankton of lakes occur just under the surface. 

 In collecting plankton, never forget to take a vertical sample tirst, but the 

 horizontal will also be very useful as a supplement. 1 am greatly inclined 

 to doubt that the plankton has a uniform horizontal distribution in all lakes. 

 In many of our lakes, the strong currents are no doubt able to cause an 

 uneven horizontal distribution. It would therefore prove interesting to take 

 vertical samples from different parts of the lake, and supply them with the 

 tow-net. 



/. Nin'cniber jo. i<Sij6. Only scattered specimens of littoral Algae. — 

 A little zooplankton, mainly- Xotliolca longispiua, ^luuræa aculeata, Anura'a 

 cochlearis, Bosniiiia obtusirostris and Nauplii. 



4. P a d d e r u d \- a n d e t is a small sheet of water not far from 

 Christiania. The surrounding area is partly cultivated slopes, partly forests. 

 — The depth is not unimportant, up to 24 m's. The geologic formation 

 is Silurian. Two samples were examined. 



/. September 2g. i8g6. I'^ertical 2j nis. — The phytoplankton mixed. 

 Pediastrum Boryanum predominating, but several other Algae in quantities. 



2. November 26. i8g6. Vertical 21 nis. Cyclotella com/a in very 

 great quantity. Only scattered specimens of other Algae. 



