Chap. I] 



THE FORMATIONS 



165 



direct rays of the sun, and should therefore necessarily assume about the same 

 temperature as the soil. Care was also taken that the seedling-trees experimented 

 with, and which stood in the forest-nursery at Mariabrunner, should be under 

 external conditions at least approximately similar to those of the different parts 

 of the crowns of trees in the forest. 



AVERAGE AMOUNT OF TRANSPIRATION FROM JUNE 1 TO 

 END OF NOVEMBER (after Von Hohnel). 



(The figures represent grams of water lost on 100 grams dry weight of foliage or needles.) 



Birch 



Lime 



Ash 



Hornbeam 



Beech 



Norway maple 



Sycamore 



Common elm . 



67-987 

 61-519 

 56-689 

 56-251 

 47-246 

 46-287 

 43-577 

 40731 



Von Hohnel came to the conclusion regarding the amount of water used by 

 a hectare 1 of beech high-forest 115 years old, that 'according to various 

 assumptions it amounts to 3.587,000-5,380,000 kilograms of water during the 

 vegetative season. A beech wood, fifty to sixty years old, during the six months' 

 vegetative season transpired 2,330,900 kilograms per hectare, and a beech-pole 

 wood, thirty to forty years old, transpired in the same period 680,000 kilograms. 1 



Since the total rainfall, roughly speaking, during the whole year amounted to 

 7,000,000 kilograms, it corresponded excellently with the results of the transpira- 

 tion obtained in the experiment 2 . 



Besides the few trees that are hygrophilous during the vegetative season, 

 and alone occur in Central Europe, there are also some that are markedly 

 xerophilous, in fact some that will thrive on the driest desert-soil. It may- 

 prove to be one of the most interesting tasks for future botanical travellers 

 to investigate the conditions of life of these markedly xerophilous trees, 

 for example those that appear in great variety in dry savannahs and in 

 tropical deserts. 



The depth of their root-system renders it possible for trees to thrive in 

 areas where long seasons of drought accompanied by great heat recur 

 periodically, as in the Mediterranean countries, in Cisgangetic India, 

 and in the Soudan. The incorrectness of the opinion frequently held, 

 that forest for its proper development requires atmospheric precipitations 

 at all seasons of the year, but especially during the vegetative season, 

 is satisfactorily shown by the occurrence of forest in regions with hot 

 dry seasons. 



77 is neither frequent atmospheric precipitation nor a rainy vegetative 



2-47 acres. 



Von Hohnel, op. cit., p. 290. 



