Soldanella Alpina. 145 



namely, to Soldanella ; and this example I select with 

 the special object of showing that the development of 

 certain protective appliances against uninvited guests 

 may, as it appears to me, even give rise to the forma- 

 tion of new species. 



Soldanella alpina L. is well known at the present 

 day as one of the most widely diffused plants above the 

 tree-Hue on the Pyrenees, Alps, Apennines, and Car- 

 pathians ; and it therefore cannot be doubted that this 

 species, as well as numerous others peculiar to the lofty 

 mountains of South Europe, already existed in the 

 region of these upheavals, at a time when glaciers 

 stiU covered the deep valleys, where wheat and maize 

 are now cultivated and where lofty trees flourish in 

 abundance. With the transition from the climatal con- 

 ditions of the ice age to those of the present milder 

 period, the above-named plant, which up tUl then must 

 have grown only in the lower situations, extended its 

 area gradually farther upwards into regions that were 

 now no longer covered with perpetual snow ; whUe the 

 situations it had hitherto occupied were at the same 

 time invaded by a number of other immigrating species. 



This advance of the boundary line of the distri- 

 bution areas must however not be conceived of as 

 a sudden occurrence, but as having been brought about 

 as gradually as the change in the climatal condi- 

 tions themselves. One plant maintained itself in the 

 valleys side by side with the new immigrants for 



