06 PERIODIC PHENOMENA OF VEGETABLE LIFE. 



My data comprise altitudes of from 1000 to 8000 feet. They 

 relate, especially as to the periods of vegetation corresponding to 

 great altitudes, to groups of mountains in and near the heart of 

 the Alps, where one meets still at a height of 4000 to 6000 feet 

 with villages, cornfields, and meadows ; as to the lower regions, 

 I have made use also of other observations made in the northern 

 portion of the Alps, and at the foot of the mountains. These 

 stations are between the 46|° and 48° of north latitude.* 



The melting of the snow and the reappeai'ance of vegetation in 

 spring, as also the commencement of the permanent winter layer 

 of snow, are periods as yet rather uncertain, yet the indications 

 given above will serve to show generally the mean commencement 

 and termination of vegetation at different altitudes. 



A very favourable circumstance in the observation of these 

 phenomena is, that the winter is so much longer in the Alps f 

 than in the plains, it commences and terminates in a much more 

 regular manner. In lower regions, and even at the foot of the 

 Alps, I especially on their southern side, the commencement and 

 disappearance of snow cannot be taken as the limits of the period 

 of vegetation, because the climate is too mild and the snow too 

 inconsiderable. The recommencement of vegetation must then 

 be determined by observation of the moment at which the 

 sap begins to flow with increased rapidity and the plant appears 

 to revivify. In climates where the winters are mild, as in 

 Belgium, for instance, it not unfrequently happens, as remarked 

 by Quetelet, § that some plants free themselves from their winter 

 sleep and continue partially to develop themselves so long as 

 there do not come on any continuous periods of frost. 



There are in the Alps considerable local irregularities in the 

 melting of the snows, according to the direction of the valleys 

 and the aspect of the declivities. Here hot banks exposed to 

 the sun are very much in advance of narrow, low, and shaded 

 valleys; there, in ravines and in the isolated depths of the valleys, 

 large masses of snow are amassed which do not melt for a very 

 long while. 



* The southern Alps are not included in the present tables. 



*r It sometimes happens in the lower regions, up to 3000 feet, that the 

 winters are interrupted by continuous south winds bringing on a general 

 melting of the snow. 



X In the lower regions, up to 2000 feet, the quantity of snow in some 

 valleys (that of the Inn, for instance, up to 1700 feet), in extreme years, is 

 not sufficient to admit of going in sledges. 



§ Phenomenes Pcriodiqties des Plantes y p. 23. 



