1 92 1. No. 4. THE PHYTOPLANKTON OF SOME NORWEGIAN LAKES. 43 



the Norwegian forms appear again in the British lakes whereas only a small 

 quantity appear again in the Danish lakes, these being of a typical Baltic 

 character. — The apportionment of the number of species among the difterent 

 groups are moreover in fair accordance with that of the British lakes. 



Of the 173 (174) species and varieties observed m are Chlorophyceæ, 

 of which there are 83 Desmidiaceæ and 28 other kinds of Chlorophyceæ, 

 19 M3'xophyceæ, 26 Diatomeæ, 8 Flagellatæ, 8 Peridineæ, i Phæophycé (and 



I Protozoan). 



Of these again 62 Chlorophyceæ are plankton species belonging to 

 groups 2 and 3, of which ^9 Dcsmidiacca' and 13 other kinds of Chlorophyceæ, 



II M3-xophyceæ, 14 Diatomeæ, 6 Flagellatæ, 6 Peridineæ, i Phæophycé 

 (and I Protozoan) total 100 (loi). The Desmidiaceæ thus constitute about 

 one half of the plankton species and varieties. 



In total the percentage of species and varieties may be apportioned 

 as follows 



,^ . Genuine British 



Plankton. Plankton. 



Desmidiaceæ 48 ^ 49 ^ 481 2 ^/0 



Myxophyceæ 1 1 ^ 11 ^/0 9 ^/O 



Diatomeæ 15 ° o 14 ^ 17^0 



Other kinds of Algæ 26 ^ 26 ^ 251 2 ^ 



As regards the distribution of the species within the Country the mate- 

 rial examined has been too incomplete to allow of more far-reaching conclu- 

 sions being put forward. 



As previously stated by far the greater part of our lakes are of the 

 Caledonian type but, besides Lake Vansjo, there are without doubt in the 

 lowland tracts of the south-eastern parts of the Countr}^ some other lakes 

 of the Baltic type. Moreover there are transition forms tending towards 

 the purely Caledonian lakes, and some of the lakes surveyed may be re- 

 cognized as being of such types. The fact that Norway lies so to sa}' on 

 the boundary between two spheres of formation would make the study of 

 the plankton of our lakes and its biology a most interesting task. 



There is however no doubt whatsoever but that the qualitati\e richness 

 of the plankton (but by no means the quantitative) increases westwards. 

 The reason for this must be looked for in the fact that the physical condi- 

 tions of the country there are more favourable, with milder winters and 

 greater rain fall. 



The distribution of the species will be best seen by the contents of 

 the big table. 1 have not ventured upon investigations based on so scattered 

 collections, to characterize some certain species as being forms, belonging 

 chiefl}- to Eastern or Western parts of the Country, nor as highland or 

 lowland forms. 



However, in order to be able to study in details the influence exerci- 

 sed on the plankton bv the different physical conditions in the various parts 



