FRESHWATER ALGÆ FROM TUDDAL IN TELEMARK. 145 



leading features of the vegetation over the wood-limit as nearly 

 always in Norway. 



The climate is as mentioned comparatively mild, but no 

 meteorological station is situated in the vicinity, so that 

 no exact data can be given. Mr. E. Roll has, however, very 

 kindly, informed me with several data, which are of great 

 interest with regard to the length of the vegetation-period of 

 the freshwater algae. — He writes that the ice of the lakes 

 breaks up as a rule in the first part of May, but often later. 

 The snow is gone about June 1., but it may be frost to the 

 end of June, and the temperature is usually lower than 

 C^ the whole day after the first of October. The snow 

 comes about the same time. It can, however, very often snow 

 in the later part of August, but Ibis snow melts soon. 



As to be seen from this, the widest limits for the period of 

 algal growth is from the middle of May to the first of October, 

 and my own experience is, that really favourable conditions for 

 algal vegetation can only be obtained from the first of July to 

 the first part of September, the algal vegetation reaching its 

 maximum in August. — Very little is known about in what 

 condition the algae survive the winter in a cold climate, (the 

 temperature in many parts of our land goes to -^ 40 C ^ and 

 temperatures of 50 0*^ below zero have been measured two times 

 at least) but it is probable that they very often pass the winter 

 in vegetative state. — The rain and snow-fall was in 1918 about 

 850 mm.i in the Tuddal valley, altitude 1430 ft. 



Tuddal is situated on the so-called Telemark-formation, 

 which is an old formation. More especially, the most of the 

 drainage area of the district investigated is situated on the very 

 hard quartzite. Formations older than Carboniferous and younger 

 eruptives are suitable for algal vegetation, more especially for 

 desmids, and this fact was confirmed by the present investigations. 



' Nedbøriagttagelser i Norge. 1918. 



Nyt Mag. f. Naturv. Lvn. 19 19. 10 



