114: NOKTH-CAKOLINA GEOLOGICAL SURVEY. 



Some elements perform a function in growth or nutrition,, 

 which is independent of nutrition in this sense, or they are 

 nutritive from their reactive forces ; they are not taken up 

 by the plant, but furnish or provide a substance by their re 

 actions upon each other, which is nutritive or administers 

 to its growth. 



These substances perform a double function ; they are really 

 nutriments, and are taken up into the vegetable tissue ; but T 

 in addition to this, their reactions upon other matters in the 

 soil are such that nutrient matter is constantly provided with 

 out their increase or diminution in the soil or marl. 



The substances which are known to perform a double office, 

 are the oxides of iron and organic matters. To enable me to 

 give a brief exposition of the functions of the oxides of iron. 

 I will state what takes place in the soil when it is well con 

 stituted for the growth of cereals, and other plants employed 

 as food. It will be observed that in the analysis of soils, the 

 iron is set down as a peroxide ; this is the state in which the 

 iron is obtained. In the best of soils the iron is not all of it 

 in this state ; but that of a mixture of the two oxides the 

 protoxide and peroxide. Now, the protoxide is changed in 

 making an analysis into the peroxide, by the addition of a 

 few drops of nitric to the hydrochloric acid, which is em 

 ployed for effecting a solution, for the purpose of obtaining 

 an exact or an uniform result. The nitric acid added to the 

 solution, is deprived of so much of its oxygen by the pro 

 toxide as is sufficient to change it, or convert it to a peroxide. 

 Now, in the ordinary course of nature, this change takes 

 place when the soil is freely exposed to the action of water 

 and air. The protoxide passes into a peroxide by the absorp 

 tion of oxygen from the water. It would remain in this state 

 permanently, if the soil was dry and free from vegetable or 

 organic matter. When soils become exhausted of these mat 

 ters, it remains a permanent peroxide. If, however, this pe 

 roxide comes in contact with organic matter, it robs the pe 

 roxide of an equivalent of oxygen, and passes again into the 

 condition of a protoxide. It is possible, therefore, for these 

 changes to take place at all times when the needful conditions 



