ABSORPTION OF HUMUS. 37 



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 favorable 

 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 19.3 lbs. over every square foot of 

 surface; 1 Hessian acre, or 26,910 square feet, con- 

 sequently receive 519,363 lbs. of rain-water. 



If, now, we suppose that the whole quantity of 

 this rain is taken up by the roots of a summer plant, 

 which ripens four months after it is planted, so that 

 not a pound of this water evaporates except from 

 the leaves of the plant ; and if we further assume 

 that the water thus absorbed is saturated with 

 humate of lime (the most soluble of the humates, 

 and that which contains the largest proportion of 

 humic acid) ; then the plants thus nourished would 

 not receive more than 330 lbs. of humic acid, since 

 one part of humate of lime requires 2500 parts of 

 water for solution. 



But the extent of land which we have mentioned 

 produces 2843 lbs. of corn (in grain and straw, the 

 toots not included), or 22,000 lbs. of beet-root 

 (without the leaves and small radical fibres). It is 

 quite evident that the 330 lbs. of humic acid, sup- 

 posed to be absorbed, cannot account for the quan- 

 tity of carbon contained in the roots and leaves 

 alone, even if the supposition were correct, that the 

 whole of the rain-water was absorbed by the plants. 

 But since it is known that only a small portion of 

 the rain-water which falls upon the surface of the 

 earth evaporates through plants, the quantity of 

 carbon which can be conveyed into them in any 

 conceivable manner by means of humic acid must be 

 extremely trifling, in comparison with that actually 

 produced in vegetation. 



4 



