10 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



found in Chapter X, with accompanying figures indicating tempera- 

 ture and precipitation in different parts of the globe, and in such 

 recognized works as W. G. Kendrew's Climatology, second edition 

 (Clarendon Press, Oxford, pp. xv + 400, 1957). The main vegeta- 

 tional types occurring on land are dealt with particularly in Chapters 

 XII, XIII, and XIV. 



Climate is the most far-reaching of the natural ' elements ' 

 controlling plant life, and its study, climatology, is accordingly 

 fundamental to plant geography and related disciplines. In the 

 words of Kendrew {I.e.), ' "Climate" is a composite idea, a generaliza- 

 tion of the manifold weather conditions from day to day throughout 

 the year. ... In the study of climatology the primary interest 

 lies in the facts of the climates of the earth in themselves, and as 

 elements in the natural environment of life.' To the phrase 

 ' throughout the year ' the ' historical ' plant geographer might wish 

 to add ' and through the ages '. 



Climatology deals with the atmospheric conditions which affect 

 life — particularly light, temperature, precipitation, evaporating power, 

 and wind. Additional factors include radiation, cloudiness, and 

 storms. These components are often interdependent, their various 

 combinations giving us the characteristic climates of different parts of 

 the world which for our purposes may be divided broadly into three. 

 These are the polar, temperate, and tropical regions, and they 

 are primarily temperature zones. For convenience, the temperate 

 areas lying north and south of the equator are considered together, 

 as are the north and south polar areas in their turn. In this book 

 the temperate regions are purposely treated first, for reasons already 

 mentioned, and are followed by the polar regions. Besides these 

 three primary categories there are the more localized climates of high 

 altitudes (whose land vegetation, being largely comparable, we shall 

 consider with that of the polar regions), of ' monsoon ' and ' Mediter- 

 ranean ' types with warm and damp seasons alternating with dry 

 ones, and of equable ' oceanic ' and widely-extreme ' continental ' 

 types {see pp. 11-12). To the three primary climatic groupings the 

 main vegetational belts of the world largely correspond, with local 

 variations engendered by localized climatic and other features. 



The climates of temperate and adjacent lands are mostly fairly 

 warm and moist, at least in the favourable periods. They exhibit 

 rather marked seasonal and diurnal fluctuations, and also vary greatly 

 from place to place. The mean of the warmest month each year 

 is normally above 10" C. (50'' F.) and the annual precipitation is 



