4 i6 ZONES AND REGIONS [Pt. Ill, Sect. II 



the greater part of Europe, West Siberia, Eastern North America, South 

 Chili, Japan, Kamchatka, New Zealand ; yet within the same latitudes 

 there are extensive districts with marked periodicity of atmospheric pre- 

 cipitation, for instance Central and East Asia and Western North America. 



The amount of precipitation in the temperate zones attains that in the 

 rainiest tropical points at only a few places. Among districts of any 

 considerable extent which have more than two meters annually there are 

 Assam, a small part of the north-west coast of America, South Chili, a part 

 of Western New Zealand ; but besides these there are only a few isolated 

 points, in particular in the Himalayas, also in the Alps, in Norway, and 

 Great Britain. Equal amounts of rainfall, however, in the temperate 

 zones, wet the soil more thoroughly than in the tropics, as they are on 

 the average spread over far longer periods of time and therefore flow 

 off to a smaller extent. 



Of great importance in the cold temperate zone is the winter snow, 

 the water melting from which is mostly acquired by the soil. 



The formation of dew is generally weaker in the temperate zones 

 than in the tropics ; fogs are characteristic of humid and cool districts, 

 near the sea in particular. 



2. SOME GENERAL EFFECTS OF THE TEMPERATE 

 CLIMATE ON PLANT-LIFE. 



i. EFFECTS OF HEA T. 



Heat, though it universally determines the very existence of plants, 

 seems to lie concealed in the tropics owing to its uniformity, and, compared 

 with atmospheric precipitations, does not essentially affect the differences 

 in vegetation either in space or time ; in the temperate zones, on the 

 other hand, differences in temperature assume both in space and time 

 a considerable importance, that rapidly increases towards the poles, and 

 finally far exceeds that of atmospheric precipitations. 



Of special significance in relation to plant-life are temperatures slightly 

 below zero, those in fact that correspond to the freezing-points of the sap, 

 which last, according to its concentration, freezes at temperatures varying 

 from a fraction of a degree to two to three degrees Centigrade below the 

 freezing-point of pure water. In the case of many plants, freezing causes 

 death from cold ; others are not indeed killed by the cold, but are injured 

 or killed by the reduced absorption of water owing to the cooling of the 

 soil, even at a temperature only slightly below zero. In Central Europe, 

 for both of the reasons given above, the earliest frosts exert a destructive 

 influence with which we are sufficiently familiar ; yet they are less 

 disastrous than exceptional frosts occurring in lower latitudes, where 



