PERIODIC PHENOMENA OF VEGETABLE LIFE. 31 



at greater elevations the melting of snows and re-appearance of 

 vegetation require a somewhat warmer temperature than in 

 lower valleys or plains. This may be caused by the circumstance 

 that, in the latter case, a partial melting of the snow has taken 

 place during the preceding months ; whilst, during the continuous 

 winters of the higher Alps, the masses of snow accumulated during 

 many months, only begin to melt away in spring ; and, as this 

 operation requires a longer time, vegetation is thereby delayed. 

 The complete melting of snow in the higher regions generally 

 takes place under the influence of warm south or south-west winds. 

 This somewhat warmer temperature, which already prevails at 

 that time at great heights, is also the cause of the well-known 

 rapid growth of meadows, and development of the first flowers of 

 Anemones, Gentians, Primula?, Tussilagos, &c., immediately after 

 the disappearance of the general mass of snow.* 



These plants begin partially to bud even earlier. The rose of 

 the Alps (Rhododendron) often makes fresh shoots under the 

 snow. The fact that, in the higher Alps, not a colder, hut even a 

 warmer temperature than in the plain, prevails at the time of 

 the melting of the snows, acts also favourably on the growth of 

 many plants at greater elevations. The snow-covering keeps the 

 temperature of the soil low, and hinders the too early shooting 

 and flowering of plants, which might be destroyed by the cold of 

 succeeding nights. Were this not the case, the constitution of 

 many plants would suffer so severely from freezing, that they 

 would probably die off, and not re-appear at the same altitude.-j- 



In later periods of vegetation, ^specially the ripening of fruit, 

 it may, nevertheless, be observed, that they take place at great 

 elevations at a lower temperature than in the lower regions of the 

 Alps. They do not even occur at the same time in the former 



* We must call to mind, also, that the rapid development of vegetation 

 in its farther progress at great elevations is also owing to the plants being 

 nearly all spring plants ; which show the same disposition when transplanted 

 into the plains. See Treviranus, Biologie, vol. ii. p. 37. 



+ An interesting phenomenon, which may be compared with the above 

 observations, is communicated by Dove, Connexion of the Variations in at- 

 mospheric Temperature with the development of Plants. Transactions of the 

 Berlin Academy for 1844, p. 341. The development of the flowers of the 

 cherry-tree in Prussian Lithuania is artificially delayed, by covering the 

 surrounding ground with a layer of non-conducting leaves, by which it is ' 

 kept longer frozen. The flowers in that case appear so late, that they are 

 no longer exposed to nocturnal frosts. In plains in general, it is of frequent 

 occurrence that trees suffer from late frosts, in consequence of the too early 

 opening of their young shoots and flowers. 



vol. vnr. 



