74 PEKIODIC PHENOMENA OF VEGETABLE LIFE. 



The mean elevation for every degree (of the centigrade ther- 

 mometer) of lowering of the temperature is in winter 670 feet, in 

 spring 510 feet, in summer 440, and in autumn 560. 



One circumstance seems of importance, which is that the lower 

 temperatures acting on plants at great elevations influence their 

 development more especially after a long lapse of time ; the period 

 of ripening the fruit, for instance, is more delayed by this 

 prolonged action than that of flowering. 



As a general mean, we find in the Alps a delay of eleven days 

 in the development of vegetation for every 1000 feet ; * this result, 

 however, shows many variations in different parts of the Alps of 

 different elevations, configuration, and aspect, on account of the 

 changes occasioned by these circumstances in the repartition and 

 fall of temperature. 



A vertical difference of 1000 feet, corresponding to a delay of 

 eleven days, entails generally in the mean temperature, especially 

 during the period when the development of vegetation takes 

 place, a difference of two degrees centigrade. 



Schuebler, from his own observations, admits, for every 1000 

 feet, a delay in vegetation of from ten to fourteen days, and a 

 difference of six days for a mean lowering of temperature of one 

 degree. 



Queteletf has confirmed these results. He finds that 100 

 metres in the climate of central Europe entails a delay of about 

 four days, which corresponds with the action of one degree of 

 latitude. | 



Thurmann has published some observations on the delays in the 

 periods of vegetation in the Jura ; he finds that, generally 

 speaking, a delay of seventeen days in the harvest corresponds to 

 a difference of altitude of 1000 feet, or 100 metres = 5 - 50 days.§ 



Some special observations, made on several points of the Jura, 

 during the first half of the summer of 1849, up to an elevation of 

 1045 metres, || gave, for the time comprised between the com- 



* Notwithstanding the variations to which these general means are liable, 

 they nevertheless serve to give an idea of general results, and to facilitate 

 their comparison in different climates. 



+ Pliinomenes periodiques des Plantes, p. 69. 



% These relations vary in different latitudes. Berghaus (Almanack 

 for 1840) observed, that between Hamburg and Christiania a much 

 shorter delay corresponds to a degree of latitude, than between South 

 Germany and Smyrna. 



§ Essai de phytostatique, vol. i. p. 51. 



|| Essai de phytostatique, vol. ii. pp. 286 — 293. These observations are 

 continued by Thurmann. 



