CHAPTER IV. 



OF THE ORGANIC CONSTITUENTS OF SOIL. 



87. The mineral elements of soil become part of plants. 

 Under the influence of the mysterious principle of life, they 

 no longer obey the chemical laws, but are parts of a living 

 structure. Life suspends all chemical laws. It organizes 

 inorganic matter. To what laws obedient, to what purposes 

 subservient, are the elements of soil during the brief moment 

 in which they are endowed with life, it is not intended to 

 inquire. Plants, by their living power, select from the sixty- 

 two elementary substances, sixteen or perhaps eighteen. Of 

 these, four exist as airs or gases in their uncombined state, 

 viz. : oxygen, hydrogen, nitrogen, and chlorine ; seven are 

 bases, and four metalloids, described (41). These fifteen 

 elements, alumina excepted, are generally constant constitu- 

 ents of plants. Iodine, once supposed peculiar to marine 

 vegetation, has very recently been found in land plants. 

 Bromine is also found in seaweed, and fluorine has occasion- 

 ally been found in the ashes of rye. 



88. Every plant does not, nor does every part of the 

 same plant contain the same elements ; but similar parts of 

 the sanie plant, at the same age, probably contain the same 

 elements, united in definite proportions. Whenever plants 

 die, their elements are again subject to the laws of aflinity, 

 and during the decay of vegetables, they return to the 

 earth not only those substances which the plants had taken 



