THE FLORA OF THE SWISS ALPS 1 



Dr. C. Schroter 

 Professor in the National Technical School, Zurich, Switzerland. 



I. 



The extensive range of the European Alps forms an arch covering a 

 distance of 750 miles from Genoa to Vienna. It comprises a series 

 of folds of geologically recent formation ; it dates from the begin- 

 ning of the Tertiary period. The Swiss Alps occupy almost the cen- 

 ter of the arch. The divisions of the Swiss Alps in horizontal re- 

 gions are determined, first, by the geological nature of the soil, and, 

 secondly, by the climate. If we glance at a geological map of the Al- 

 pine range showing a few outlines, we perceive a center of primitive 

 siliceous rocks, the Central Alps. This center is bordered on the 

 south and on the north by a fringe of calcareous sediments, first of 

 Mesozoic, then, toward its margin, of Tertiary age. The Prealps are 

 therefore formed principally by calcareous soils, nourishing a cal- 

 ciphilous vegetation ; the Central Alps consist of siliceous rocks, oc- 

 cupied by a limestone-avoiding flora. 



In addition to this geological difference between Central Alps 

 and Prealps, we have a climatical one in this sense, that the Prealps 

 show a more oceanic climate with mitigated extremes, the Central 

 Alps are more continental with pronounced extremes. This accounts 

 for the fact that the two trees of continental character, the Larch 

 (Larix decidua Mill.) 2 and the Stone or Arolla Pine (Pinus cembra 

 L.), are confined to the Central Alps. 



A third difference between Prealps and Central Alps is account- 

 ed for by the difference in altitude of the upper limit of the growth 

 of trees and of the under limit of eternal snow. It is a general law 

 that in great mountain masses all limits are found at a higher level 

 than in isolated chains. (This is clearly indicated by the picture 

 showing the situation of the snow-line in the different parts of Swit- 

 zerland. All the points with identical altitude are joined by a black 

 line, called an isochion.) In the region of the northern Prealps the 

 snow-line lies at 8,000 feet, and toward the Central Alps it rises 

 higher and higher; in the Engadine Alps it is situated at 9,300 to 

 9,600 feet, in the great masses of the Pennine Alps ( Monterosa ) 

 even at 10,000 feet. Similar differences show the upper limit of tree- 

 growth, and in general all the limits of plant life. 



From this fact, combined with the warm summer and historical 

 causes, originates the great variety of the flora of the Wallis and the 

 Engadine ; if you want to spend your holidays in the countries rich- 

 est in alpine flowers, you are to go to Zermatt or to Pontresina. 



lecture delivered before the Society, Sept. 12, 1913. 



2 Nomenclature after Schinz and Keller, Flora der Schweiz, 3 ed. 1909. 



