44 



just as in the domain of physics Irom Ihe same reasons Ihe com- 

 mon gas laws are not valid ior verv small (juantities of a gas. 



Some years ago, there was a pronounced maximum in the num- 

 ber of voles on Svartlöga. In the spring of 1915, almost all 

 fruit-trees on the island stood loose in the ground and låter died 

 because their roots had been eaten through by the voles during 

 the Avinter. In the same summer, the observation was made that 

 Sphagna had come into the meadows and meadow-woods, occur- 

 ring in a very peculiar manner, viz. forming an irregular mosaic 

 and stripes in the shape of a system of veins on certain spols of 

 the grass lawns, A nearer invesligation showed that on the spöts 

 mentioned the ground was almost completely undermined by the 

 voles, and the system of Sphagnum veins corresponded to a system 

 of real veins in the ground, mined by the voles. 



As to the causal relation between the two effects, il seems unli- 

 kely to suppose that the mining of the voles should locally cause 

 an increased humidity in the ground. The more probable con- 

 jecture is, I believe, that the peat-moss could come in simply 

 because the grass-roots wore eaten up and the grasses killed by 

 the voles. It may be supposed that on the moist meadows of 

 Svartlöga, in a humid sea-climate, the advantage in the competi- 

 tion between the grass vegetation and the peat-moss is always but 

 slight in favör of the former, so that a slight injury befalling Ihe 

 successful competitor may give the other one the advantage. 



The phenomena observed, however, Avere but temporary. In 

 the foUowing years, the peat-mosses have again disappeared and 

 so have the voles almost completely. The latter fact is probably 

 caused partially by the weather in the spring of 1916, which was 

 not suilable for their young, on the other hand by the bringing in 

 of hedgehogs {Erinaceus eiiropaeiis). 



The fact that the Sphagna disappeared as quickly again as Ihey 

 did, would perhaps permit a conclusion that goes against the con- 

 cepts of Palmgren on competition in the islands of Åland only a 

 few miles distant from Svartlöga. This author concludes from 

 certain facts (the chief of which I have critizised elsewhere from 

 another point of wiew; Romei.l 1920) that the ecological factors 

 have little or no importance for the distribution of plants in the 

 meadow-woods of Åland, so that competition there would be merely 

 a contest of being the first on a free place. The rapid appearence 

 and disappearence of the Sphagna under the conditions described 



