Lirmaan Society. 347 



the form of the mountain-range, the limits of vegetation being 

 generally connected with the mean magnitude of the elevation, and 

 reaching higher in massive and lofty groups of Alps than in the 

 lower chains. The favourable influence which the massiveness of 

 the elevation exercises on the vegetation, is essentially the same as 

 that which is also evidenced with regard to the temperature of the 

 air and soil ; and corresponds to the difference which is remarked 

 between the climate of a plateau, and that of a ridge or free peak in 

 the neighbourhood. In different valleys or on the spurs of a moun- 

 tain remarkable difl^erences in the altitude of the limit of vegetation 

 often manifest themselves according to the exposure, the direction 

 of the ■wind, or the proximity of separate and extensive masses of 

 glacier ; but these influences are for the most part merely local, and 

 the general variations of the limit of vegetation dependent on the 

 massiveness of diff^erent groups of Alps are but little affected thereby. 

 A comparison of the annual isotherms with the limits of vegetation 

 proves that the different groups of vegetation do not always 

 terminate at the same annual isotherm. With the exception of 

 the Beech, he showed that up to the height of Conifer a, these 

 limits in the Northern Alps are reached at warmer isotherms than 

 in the Central Alps , and a somewhat lower mean temperature 

 is observed on corresponding points of the group of Monte Rosa and 

 Mont Blanc. This is immediately dependent on the fact that the 

 growth of plants is not determined alone by the mean temperature 

 of the year, but also by that of the seasons and of the months. The 

 warmth of the summer is in this view of peculiar influence ; the 

 g/eater this is in connexion with the same mean temperature of the 

 whole year, the higher plants ascend, and the colder are the annual 

 isotherms which mark their limits. A review of all the meteor- 

 ological observations made in the district of the Alps shows that in 

 the Central Alps and in the group of Mont Blanc and Monte Rosa, 

 the summer warmth is greater and the climate consequently more 

 extreme than in the lower chains of the Northern Alps ; by which 

 means the relation of the limits of vegetation to the annual isotherms 

 in these different mountain-groups is explained. 



He further stated that his and his brother's investigation of the 

 periodical development of the vegetation at heights of from 1500 to 

 8000 Paris feet showed among other things that the retardation of the 

 development by the elevation is in general less during the flowering 

 than during the ripening of the fruit ; it amounts in the Alps during 

 the former period to ten days, during the latter to twelve and a half, 

 and on the average of the whole period of vegetation to eleven days. 

 The mean temperature is diminished in general about 2° of Celsius 

 for the same difference of height, during the period of the develop- 

 ment of vegetation. From their own observations on the influence 

 of height on the growth of Coniferce, he concluded that in Pinus 

 Larix, P. Abies, P. sr/lvestris and P. Cembra, an evident diminution 

 in the thickness of the annual rings takes place at greater elevations. 

 A regular diminution, however, must not be expected for each 

 degree of elevation. Not only the variations in the temperature of 



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