826 ASTRID CLEVE, THE PLANKTON OF SOME LAKES IN SWEDEN. 



As regards the seasons when tlie plankton was gathered, I 

 have collections from Lilla Lulevattnet taken both in spring 

 and in autumn. The former were gathered in the middle of 

 June at a time when the upper lakes Skalka and Saggat had 

 just got free from ice, owing to the late spring that year. 

 Nearly three months låter, in the beginning of September, I 

 collected the autunin-plankton when I was leaving for home. 

 The considerable difierence between the two sets of plankton 

 thus gathered at an interval of three months will be clearly 

 seen from the following. 



From Virijaure I have but one set of plankton, all gathered 

 in the beginning of July. It may be considered as repre- 

 senting the early spring-plankton of the lake, which, at that 

 time, was still to a great extent ice-bound in its western bays. 

 I greatly regretted the irapossibility of getting Virijaure-plankton 

 of a låter season, but after the Laplanders had left the eastern 

 bays, no boat could be found in the neighbourhood. 



The collections were all gathered in the same way, by drag- 

 ging a conical tow-net behind a slowly paddled boat, so as to 

 keep the net just beneath the surface of the water at a depth 

 that does not, as a rule, surpass one meter. The time neces- 

 sary for each gathering varied greatly according to the frequency 

 of the plankton. In spring, the water was very poor, especially 

 in Virijaure, where the tow-netting had to be kept on during 

 hours before a sufficient material could be obtained. The autumn- 

 plankton from the lakes in the forest-region on the contrary 

 occured so abundantly, that a coUection of several ccm. could 

 be made in a few rainutes. Still no visible fl o atin g- plankton, 

 no flos aquce was observed anywhere. 



I. a. Spring-plankton from lakes in the forest-region. 



1. Vaijkijaure ^Ve 1896. 



Plankton rather scarce, mostly animal forms (crustaceans 

 and rotatorians), less frequent diatoms. 



