^49 



NOTES AND COMMENTS. 



INFLUENCE OF TECTONIC FACTORS ON VEGETATION. 



The recently published Part XL of ' Die Vegetation der 

 Erde,' has been noticed at some length by Dr. Wm. G. Smith 

 in the May number of the ' Scottish Geographical Magazine,' 

 and some of the features dealt with are well worth the attention 

 of all interested in problems of plant distribution. This part 

 deals with the vegetation of the Balkan lands, and is by Dr. 

 Lujo Adamovid. A noteworthy feature of this work is the 

 importance ascribed to the influence of tectonic factors in 

 vegetation ; that while climate and soil conditions play an 

 important part, yet neither alone nor combined do they entirely 

 determine vegetation. The influence of mountains as barriers 

 to climate has its effect on the vegetation, and the winds pre- 

 vailing in a valley must bring distinct conditions. Mountains 

 and valleys are routes of migration for plants, because some- 

 where, high or low on the slopes, any given species can find 

 those conditions best suited for its full development and repro- 

 duction. A long simple mountain range, without lateral spurs 

 or broad intersecting valleys, is well adapted to act as a bridge 

 for migration, but the number of species will probably be small 

 because the slopes are everywhere exposed. 



INFLUENCES OF THE 'MASSIF.' 



The conditions on a mountain ' massif ' are different, spurs 

 branch off in many directions, thus affording much variety in 

 exposure and shelter, and favouring a greater number of species. 

 The mass is less liable to extreme climatic conditions, and in 

 Servia the presence of grouped mountains furnishes the lower 

 lands with moisture, an important item in a region of summer 

 drought ; a longer winter also results, but this furnishes con- 

 ditions suitable for the growth of species requiring moisture and 

 a cool climate. 



WIND versus temperature, etc. 



In a great ' massif,' too, all the zonal limits of plants are 

 lifted upwards, and cultivation of crops is carried higher than 

 it is on long open ranges. Dr. Adamovic attributes this to 

 wind more than to temperature and soil. The higher and more 

 complex the mountain group, then so much higher lies the most 

 destructive sphere of the wind, hence there is for plants a 

 greater available area with a favourable environment, including 

 suitable insolation, soil- warmth and soil-moisture. The 



1910 July I. '^ 



