82 PERIODIC PHENOMENA OF VEGETABLE LIFE. 



case, but later during the period of decreasing temperature. As 

 a fine example, we may take the case of the Cherry and of the 

 Winter Rye. 



The Cherry ripens 



In Western Europe, in general, according to Gasparin,* 



at a mean temperature by day of 17°, Scent. 



In East Prussia, according to Dove,-j' at a temperature 



by day of 17°, 5 cent. 



At tbe foot of the Alps, to the height of about 2000 feet, 



it appears likewise to range between 17° and 18° 



Towards the upper limits of the tree in the central Alps, 

 at 4500 feet, where the ripening only begins on 

 20th August the temperature during the period 

 does not exceed 11° to 12° 



The Winter Rye ripens 



In East Prussia, according to Dove, at 17°, 9 cent. 



At the foot of the Alps, the temperature is nearly the 

 same. At the upper limits of its cultivation in the 

 higher chains of the Alps, at an elevation of 5200 

 feet, the temperature at the time of ripening on 

 3rd September is barely 10° 



Whilst a considerable diminution is apparent at lower 

 altitudes of 4000 to 4500 feet. 



In the case of the Grape-vine, also, the ripening takes place at a 

 much lower temperature towards its northern limits, as well as 

 towards its limits in altitude, than in more favourable situations. 



In considering the total temperature during the whole period of 

 vegetation of a plant, or during particular periods of development, 

 we must distinguish those temperatures which are directly pro- 

 motive of vegetation, and those which occasion their growth to 

 remain stationary. In mean temperatures, as they are usually 

 taken, these considerations cannot be completely comparable, as 

 the temperatures below the freezing point have in the averages 

 the same value as those above it ; that is not, however, the case 

 with plants, as growth only takes place with the higher tempera- 

 ture. The lowering of the temperature may, indeed, produce a 

 stoppage in growth, or even the death of the plant ; but there is 

 never any retrograde step in the only sense in which it can be 

 compared to temperatures below freezing point, and to the 

 manner in which they are taken account of in striking the 

 monthly and annual means. 



The temperature at which the development commences, as 



* Cours d' Agriculture, vol. ii. p. 94. 



t Reports of the Berlin Academy, 1850, Table 2, at p. 214. 



