42 



KAARE MUNSTER STRØM. M.-N. Kl. 



tliroii}^li()ut llic uliolc temperate part of the world, where the physical 

 conditions of the districts are suitable to its development. 



Some authors are disposed to ronsider it a phenomenon of Culture caused 

 by contamination of the water from cultivated areas and human dwellings. 



To what extent they are right it is hard to tell ; it nmst be considered 

 certain that a serious contamination renders the development of plankton 

 Desmidiaceæ impossible (excepting Stattmstrum gracile and Stnurastrum 

 paradoxmn and a couple of tycholimnetic Clostcria). Such contamination 

 also supports the development of some certain kinds of semi-saprophytic 

 Myxophyceæ and other Algæ. 



The term Caledonian was suggested by Ti;ii.i.\(. and it appears to me 

 that biologists should accept same as a designation for the formation whose 

 composition has essentially been made clear througli Messrs. West's work 

 in Scotland (Caledonia) ^ 



Moreover, its central distribution comes within the folding system which 

 the geologists call the Caledonian. 



As far as we know, this formation is frequently found, provided that 

 the physical conditions of the country are favourable, in lakes in large parts 

 of Sweden (possibly in Finland), in Norway ^, the Færo Islands, partly in 

 Iceland, in Scotland, the Shetlands, the Orkneys and the Hebrides, the English 

 Lake District and Ireland, in greater or smaller quantities according to the 

 physical conditions. 



Likewise plankton of essentially the same composition occurs in Spain. 

 — It may be that plankton of a similar composition occurs in Greenland 

 and the Arctic America; over large parts of U. S. A. such plankton is fre- 

 quently found (according to Prof. G. M. Smith's researches), and there it is 

 also mixed with special American forms. It is very likely that such plank- 

 ton will be found generally in the Canadian lakes. 



The plankton in some certain of the Alpine lakes is also said to be 

 rather rich in Desmids but they do not belong to the Caledonian type, nor 

 do they occur in anything Hke the quantities in which these occur. 



If we now take a glance at the Norwegian plankton as same presents 

 itself according to Huitfeldt-Kaas and the present investigations it be- 

 comes evident that all the lakes examined are of a more or less Caledonian 

 type (save Lake Vansjo with Baltic plankton). 



The composition of the plankton is however extremely variable in the 

 various lakes and in very few places Desmidiaceæ are so plenty as in the 

 Scotch lakes though the leading Caledonian forms are present in most cases. 



The geographical affinity of the plankton is a fact which can be proved 

 best by studying the two last columns in the summary table. Neariy all 



' Exhaustive list of literature as an appendix. 



2 I have just received collections from Lake Oksefjordvand I71O N. L.I, probably the most 

 northern lake in this Country; in these collections there are various Caledonian plank- 

 ton Desmids in large quantities. 



