Chap. I] 



THE FORMATIONS 



J 75 



timber-forest I must estimate much lower l . ... If we glance over the results 

 obtained in the above paragraphs, we cannot help expressing the opinion that 

 an extreme continental climate is unfavourable to tree-growth, iv/iic/i can only attain 

 its maximum development in a maritime climate 2 .' 



The woodland-climate in its various gradations and the grassland- 

 climate remain qualitatively the same in all the zones, but differ 

 quantitatively from one another, so that their elements can be expressed 

 numerically only for each zone treated separately. The meteorological 

 tables on which the opinions here developed are based are therefore 

 relegated to a later part of this book 3 . 



iv. METEOROLOGICAL TABLES. 



The number of districts for which really useful and complete meteoro- 

 logical observations, extending over prolonged periods, are available, is 

 not yet considerable. Yet in reference to several regions, that are well 

 characterized both as regards their climate and vegetation, there are 

 already data which are sufficient in both these respects as a foundation for 

 general conclusions. Meteorologists do not always take into consideration 

 all the factors that concern the climatic knowledge of vegetation ; though 

 this is partly the fault of geographical botanists, who formerly made 

 very modest demands on meteorology owing to their misapprehension 

 as to the significance of many climatic elements. 



A Table really fit for use from a phytogeographical standpoint should, in my 

 opinion, contain the following headings: — 



Longitude 



stations) . . 



Latitude 



LOCALITY , 



. . ; Altitude 



Mean Barometric pressure (only at high 



Temperature. 



Months. 



Rainfall. 

 Amount. Days. 



Relative 

 humidity. 



Sunshine. 

 Hours. 



Strength 

 of wind. 



Evapora- 

 tion. 



Mean Mean Amount. Days. Mean Mean 

 Min. Max. Min. Max. 



Jan. . 

 Feb. 

 Mar. 



&c. 

 Mean annual extremes 



The variations in the atmospheric pressure carefully noted by meteorologists 

 are devoid of significance to vegetation. Of the data regarding temperature, 

 those of the daily minima and maxima are the most important, in fact quite 

 sufficient. Records of the hours of observation are hardly necessary, since the 

 minima occur at night and the maxima during daytime. The former give us the 

 temperatures at which the processes of growth chiefly occur, the maxima are 

 especially important as factors influencing transpiration. The mean diurnal 



1 Middendorff, op. cit., p. 632. 



Id. p. 640. 



See Part, III. 



