ABSORPTION OF HUMUS. 11 



Again, if the quantity of humic acid which might 

 be introduced into wheat in the form of humates is 

 calculated from the known proportion of metallic 

 oxides existing in wheat straw, (the sulphates and 

 chlorides also contained in the ashes of the straw 

 not being included,) it will be found that the wheat 

 growing on 40,000 square feet of land would receive 

 in that way 57i Ibs. Hessian of humic acid, cor- 

 responding to 85 Ibs. Hessian of woody fibre. But 

 the extent of land just mentioned produces, in- 

 dependently of the roots and grain, 1780 Ibs. 

 Hessian of straw, the composition of which is the 

 same as that of woody fibre. 



It has been taken for granted in these calcula- 

 tions that the basic metallic oxides which have 

 served to introduce humic acid into the plants do 

 not return to the soil, since it is certain that they 

 remain fixed in the parts newly formed during the 

 process of growth. 



Let us now calculate the quantity of humic acid 

 which plants can receive under the most favour- 

 able circumstances, viz. through the agency of 

 rain-water. 



The quantity of rain which falls at Erfurt, one 

 of the most fertile districts of Germany, during the 

 months of April, May, June, and July, is stated 

 by Schubler to be \7\ Ibs. Hessian over every 

 square foot of surface ; 40,000 square feet con- 

 sequently receive 700,000 Ibs. Hessian of rain- 

 water. 



