Ch.VI] cold temperate WOODLAND AND GRASSLAND 555 



1. The differentiation of the vegetation in the cold-winter belts is simpler 

 than in the warmer belts, as there is scarcely any difference between 

 hygrophilous and xerophilotis forest, and, except on high mountains, climatic 

 shrub-formations do not occur. Thus only forest and grassland — the 

 latter as meadow or steppe, never as savannah — stand opposed to one 

 another. 



2. The amount of rainfall necessary for the existence of forest varies, in 

 any case, according to the temperature and dryness of the summer ; over 

 a great part of Europe, its lower limit may be 50 cm., but in North 

 America, where the summers are hot, the limit is somewhat higher. 

 Factors favourable to good tree-growth are specially a winter with abundant 

 rain, comparatively free from wind, and, in particular, with no dry winds 

 blowing during hard frost, and further, a summer devoid of hot dry winds. 



3. Owing to the shortness of the vegetative season, an annual rainfall of 

 30-40 cm. appears sufficient for grassland in the form of steppe, provided 

 it falls chiefly in spring and early summer and is as evenly distributed as 

 possible. Climatic factors that are hostile to trees are without influence 

 on grassland. 



4. When the rainfall is less than 30 cm., or even when it is somewhat 

 greater but at the same time occurs chiefly in winter or is evenly dis- 

 tributed throughout the year, the vegetation assumes the character of that 

 of desert. 



SELECT LITERATURE. 



The general climatic characteristics are taken from Hann's Handbuch der Klimato- 

 logie, ed. 2, Vol. Ill, and from the same author's Atlas der Meteorologie, 

 Gotha, 1887 ; those for Russia from Woeikof's Die Klimate der Erde, Jena, 

 1887. 



Hann, J. I. Handbuch der Klimatologie. Aufl. 2, Bd. I— III. 1897. 



II. Die Vorschlage zur Milderung der Sommerdurre in Ungarn. Zeitschrift 



der osterr. Gesellschaft fur Meteorologie. Bd. II. 1867. 

 Hunfalvy, J. Die klimatischen Verhaltnisse des ungarischen Landercomplexes. 



Ibid. 

 Peschel, O. Physikalische Erdkunde. Bd. I— II. Aufl. 2. 1883. 

 Woeikof, A. Die Klimate der Erde. Bd. I— II. Jena, 1887, 



