166 FORMATIONS AND GUILDS L Part n 



season that is of importance to tree-growth, but it is the continuous presence 

 of a supply of water within reach of the extremities of the roots, and 

 therefore at a considerable depth in the soil. It is immaterial during 

 what season this supply is renewed. There arc forest districts with rain 

 at all seasons of the year and others with dry seasons. In districts with 

 dry seasons the rainy season may mainly or entirely coincide with the 

 vegetative season, as in the tropics or the interior of Argentina, or the 

 rainy season may coincide with a season that is relatively one of rest 

 for vegetation, as in extra-tropical districts with winter rain, including 

 Mediterranean countries, the South Caspian district, Chili, California, 

 South-west and South Australia. 



The trees of a forest district with a dry vegetative season are 

 dependent on water-supplies, collected during winter, and occurring at 

 a considerable depth ; they have corresponding characteristics. Their 

 root-system penetrates deeply into the soil and is strongly developed, 

 the stem and roots are frequently furnished with apparatus for storing 

 water, the foliage is protected against rapid loss of water in hot dry air. 

 In districts without a markedly dry season, or where this is at the same 

 time a period of rest for tree-vegetation, the trees possess less perfect 

 absorptive and protective contrivances. The foliage is delicate and tran- 

 spires freely, the whole character is hygrophilous, but yet, in abnormally 

 dry seasons, even hygrophilous trees, like all deep-rooted plants as 

 opposed to shallow-rooted ones, show remarkable powers of resistance. 



Thus during the rainless vegetative season of the year 1893, along the 

 Rhine and in Western Switzerland, meadow grass grew to a quite inconsider- 

 able height only, and most perennial herbs in the meadows completely dried 

 up before the end of June. Above the low straw-coloured sward of the 

 meadows, lucerne, sainfoin, and other deeply rooted perennial herbs stood 

 out as fresh, sap-green, luxuriant bushes. The foliage of trees only in July 

 became partially dry, and the fruit was as succulent as usual and grew to 

 its ordinary size. Considerable supplies of water provided by the winter 

 rain, therefore, still remained stored in the soil, though only accessible to 

 deeply rooted plants. Yet here we are dealing with a vegetation that 

 is hygrophilous during the summer and under normal conditions is not 

 exposed to drought associated with a high temperature. 



Important observations regarding the significance of the amount of 

 rainfall and winter rain to the forest have been communicated by 

 Woeikof: — 



' I will not deny the influence of summer rain on forests, as on all other kinds 

 of vegetation, but atmospheric precipitations falling in the cold season, especially 

 when they occur in the form of snow, are far more important. Forests require 

 a continuous supply of water in the stratum containing their roots, in order to 

 balance the continuous evaporation from the leaves. The colder the season is 



