84 PEKIODIC PHENOMENA OF VEGETABLE LIFE. 



are items of great importance.* It appears, nevertheless, that in 

 considering the influences of different latitudes and altitudes, the 

 sums of temperatures, or, as Quetelet proposed, the sums of the 

 squares of temperatures f give very fair general points of 

 comparison. 



If we investigate these conditions according to either of these 

 modes of computation, we shall find that many plants, at their 

 highest limits in the Alps, notwithstanding a considerable retarda- 

 tion of their periods of vegetation, experience a less total heat for 

 the same stages of development than in plains. J In this respect, 

 we might especially have made use of meteorological observations 

 taken in the years 1 848-49 at Vent, Heiligenblut, and Sagritz, 

 in connexion with memoranda on the development of plants. 

 But the period of time appeared to us to have been too short to 

 give specifically the figures which resulted from them, as 

 differences in different years are so important, according to the 

 interesting communications of Dove.§ The diminished total heat 



* A. de Candolle attempted to make use of the development of single 

 plants, in conjunction with the temperature in sunshine and in shade, for 

 the appreciation of the development of vegetation in general, and at 

 different seasons of the year. Bibl. de Geneve, 1850. Sciences Physiques, 

 pp. 177—192. 



+ Hess of Stettin has shown that relative moisture may also be taken in 

 account by dividing the product of heat and time by the relative humidity. 

 Lamont (Annals of the Observatory of Munich, 1849, p. 171) remarks, that 

 a more correct result will be obtained by combining higher powers of the 

 mean temperatures with the squares of the extremes. The farther 

 removed the phenomena considered are from the commencement of vege- 

 tation in spring, the more concordant will be the results obtained by 

 different methods, because during the longer periods single variations 

 compensate each other more and more. 



J That vacillations in the total heat are not uninfluenced by the nature 

 of the plants themselves, is shown by A. de Candolle's observations. It 

 appeared that, even with the most careful experiments with seeds of the 

 same kind, the total temperature under apparently similar outward cir- 

 cumstances was never precisely the same ; single plants were developed, 

 some more rapidly, others more slowly. Bibl. Universelle, 1850, p. 179. 



§ According to Vogt's observations at Arys, in East Prussia, comprising 

 the years 1836 to 1849 (Reports of the Berlin Academy, 1850, p. 213), the 

 differences in different years, that is, the non-periodic variations in tem- 

 perature, become, as shown by Dove, important in another way. There 

 frequently occurs a succession of favourable or unfavourable years ; if the 

 first development of a plant occurs during a series of favourable years, it 

 may reach such a size that its existence is secured, also, for succeeding 

 years ; this is an important point for acclimatising and other experiments in 

 cultivation. These conditions may also have been of great importance in 

 the case of isolated trees at great elevations, which may be often found at 

 considerable distances from all others. If once they have been able to 



