90 PERIODIC PHENOMENA OF VEGETABLE LIFE. 



period of vegetation to a mean of eleven days. The mean tem- 

 perature for the same difference in height, especially during that 

 season when the development of vegetation takes place, experiences 

 a diminution of 2° centigrade. 



1. The temperature at which a given phenomenon commences, 

 appears generally in spring to remain nearly the same at different 

 elevations ; the melting of snow, however, and the first awakening 

 of vegetation take place at great heights, at a somewhat higher 

 temperature. For the periods of fruit ripening, on the contrary, 

 it is clearly observable that it takes place at great heights at a 

 lower mean temperature. The differences for many plants are 

 considerable. It amounts, for instance, in the case of the Cherry, 

 to 5° or 6° centigrade, in that of Winter Rye to near 8°, on a 

 comparison of the highest points where it is grown, with the foot 

 of the Alps or the plains of Germany. 



5. Whether we take the sum of the temperatures or the sum 

 of the squares of temperatures between the different periods of 

 vegetation, it will appear by either method, that many plants at 

 their highest limits in the Alps experience a lower aggregate 

 temperature for the same stages of development than in the 

 plains ; this is more especially apparent in the case of Cereals. 



6. By a comparison of separate stations in the Alps, it appears 

 that many aberrations in the periods of vegetation are occasioned 

 by the repartition of the temperature in the several months or in 

 shorter periods. Between points which have the same altitude 

 and mean temperature, those whose climate is more extreme are 

 always more forward in their vegetation than those where the 

 variations of temperature are less. 



7. The product in grain of Cereals, as well as the quality and 

 the proportion in weight to that of the straw, diminishes with 

 altitude ; the former in the case of Winter Rye and Barley, at their 

 outer limits of cultivation from 5000 to 5200 feet, sinks, even 

 taking the mean of the most favourable year, to from twice to 

 three and a half times the seed. An increase of temperature 

 during the period of vegetation at great heights increases the 

 produce with great regularity ; and in such situations, fruitful 

 years generally coincide with those in which the ripening of the 

 fruit is in advance of the mean period. 



