ABSORPTION OF HUMUS. 9 



therefore are destructive of the solubility of humic 

 acid, and at the same time of its capability of being 

 assimilated by plants. So that, if it is absorbed by 

 plants, it must be in some altered form. 



The correctness of these observations is easily 

 demonstrated by treating a portion of good mould 

 with cold water. The fluid remains colourless, 

 and is found to have dissolved less than 100,000 

 part of its weight of organic matters, and to 

 contain merely the salts which are present in rain- 

 water. 



Decayed oak-wood, likewise, of which humic acid 

 is the principal constituent, was found by Berzelius 

 to yield to cold water only slight traces of soluble 

 materials; and I have myself verified this observa- 

 tion on the decayed wood of beech and fir. 



These facts, which show that humic acid in its 

 unaltered condition cannot serve for the nourish- 

 ment of plants, have not escaped the notice of phy- 

 siologists ; and hence they have assumed that the 

 lime or the different alkalies found in the ashes of 

 vegetables render soluble the humic acid and fit it 

 for the process of assimilation. 



Alkalies and alkaline earths do exist in the dif- 

 ferent kinds of soil in sufficient quantity to form 

 such soluble compounds with the humic acid. 



Now, let us suppose that humic acid is absorbed 

 by plants in the form of that salt which contains 

 the largest proportion of humic acid, namely, in the 

 form of humate of lime, and then from the known 



