2 O. W. Arrhenius 



and replaced. The humus also was sieved and replaced on top of 

 the mineral soil. The corners of the area were marked with poles. 



This bare area, of course, had not the same properties as the 

 old soil; many of the factors were changed in one direction or 

 the other. 



These areas were visited in 1922, 1924, and 1932. 



The district of these investigations belongs to the most arid 

 region of Sweden. The annual rainfall is low — from 300 to 

 400 mm. The moisture of the air is rather high, but the evapora- 

 tion is strong because of the hard and everlasting winds. The 

 water is the dominating factor. 



Tables i to 6 (below) present the results of the investigations. 



The figures give the real numbers of the plants in each square 

 meter. As a plant the section between the soil and a stem has 

 been counted. When it is possible and of interest, the location 

 of the different plants is given on a map. This shows the number 

 of plants of different species in every small square. The expla- 

 nation of the signatures is found in the tables; for example, V5 

 in table i marks 5 Vaccinium vitis idaea. 



From the tables, we see that the plant migration is going on 

 very slowly, especially where the soil is dry. The most extreme 

 condition we find in table 3, where the plants have not succeeded 

 in establishing themselves after twelve years. 



Most interesting to see, however, is how the migration goes on. 



The migration has always taken place from the border. It is 

 those squares which are situated next to the old vegetation which 

 show new vegetation. And where the areas are subject to a 

 prevailing wind — from the shore — we see that the migration 

 chiefly has taken place from the windward side. 



The long-distance migration must be of very small importance 

 in these associations. 



