CHAP. V.] 



Soil and Situation 



93 



of fungoid diseases whilst growing, or of red and white rot after 

 conversion. According to Weber 1 , the analyses of different 

 woods show that the composition of timber consists, on a rough 

 average, of 50 % Carbon, 42 % Oxygen, 6 % Hydrogen, i % 

 Nitrogen, and i % Ash only, for a great many of the mineral 

 constituents abstracted from the soil are deposited in the 

 foliage during the process of preparing the food- supplies 

 for assimilation, and are returned again to the soil when 

 defoliation occurs, and the dead foliage decomposes into 

 humus or mould. But the whole demand for mineral food 

 made by woodland growth is, roughly speaking, only about 

 one-half of what it amounts to in the case of agricultural 

 crops, according to the investigations made by Ebermayer 2 , 

 which may thus be tabulated : 



As, in sylviculture, the greatest demands are for lime and 

 silica, constituents abundant in every soil, and, as by the fall 

 of the leaf, most of the mineral food is returned to the soil again, 

 it will be at once apparent that woodland growth does not 



1 DieAufgaben der Forstwirthschaft (Lorey's HandbucK}, p. 62. 



2 Physiologische Chemie der Pflanzen, 1882, vol. i. p. 761. 



