i66 FORMATIONS AND GUILDS [Part II 



season tliat is of iniporlance to trec-growtJt, hut it is the continuous presence 

 of a supply of ivater ivitJiin 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 are forest districts z^'ith rain 

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

 dry seasons tlie rainy season may mainly or entirely coincide ivith the 

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

 rainy season may coincide icith 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. Theirj 

 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 perfeclj 

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

 spires freely, the whole character is hygrophilous, but yet, in abnormal!) 

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

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



Thus during the rainless vegetative .season of the year 1H93, along thi 

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

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

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

 meadows, lucerne, sainfoin, and other deeply rooted perennial herbs stoo( 

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

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

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

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

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

 is hygrophilous during the summer and under normal conditions is nc 

 exposed to drought associated with a high temperature. 



Important observations regarding the significance of the amount c 

 rainfall and winter rain to the forest have been communicated b 

 Woeikof : — 



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

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

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

 a continuous supply of water in the stratum containing their roots, in order 1 

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



