1847.] Ploiving and Hoeing. 161 



stand what these changes are, it becomes necessary to speak of 

 some of the elements ot the soil; for the simple presence of more 

 air in the interstices of the soil is not in itself suthcient. We do 

 not know that the spogioles of the roots can take in air or oxy- 

 gen, or even carbonic acid, so long as they remain gaseous, or 

 rather, uncombined with other bodies. We believe, at any rate, 

 that these gaseous bodies, before they are received into the tissue 

 of the plant, must be dissolved in water, or enter into combina- 

 tion with the elements of the soil. 



The element which performs an important, not to say the most 

 important function, is iron. It exists in two forms, a protoxide 

 and peroxide: and it is probable that all soils contain it in both 

 states, at the same time. Now the important fact which comes 

 out of these two states, is this, viz., that plants possess the power 

 of taking away from the peroxide an atom of its oxygen, when 

 it will be reduced to the state of a protoxide; or if living plants 

 have not this power, organic matter in the soil has. So that the 

 iron, in its state of peroxide, is continually being reduced to its 

 first state of oxidation; by which change it is furnishing oxygen 

 either to the growing plant, or else furnishes it to the dead inor- 

 ganic matter; by which it becomes an organic acid, and capable of 

 combining with the alkalies and alkaline earths. These are 

 then prepared to be received into the tissues of the living plant, 

 by which it is nourished and matured. But the protoxide of iron 

 does not long remain in this state. It soon takes again from the 

 atmosphere another portion or atom of oxygen, and, as it would 

 seem, only to be robbed again by the organic matter of the soil. 

 Now, plowing and hoeing aid these changes: for free exposure 

 to the atmosphere facilitates the oxidation of the iron; and to im- 

 proved plants it becomes a necessary part of their cultivation; if 

 we would forward their growth, we must facilitate also the round 

 of these chemical actions. 



But again, iron does not act upon the air alone; it decomposes 

 water also. It robs water of its oxygen, as well as the atmo- 

 sphere. This chemical change, in fact, is more important than the 

 other; for, involved in this decomposition, is the formation of one 

 of the most important bodies to vegetation. We allude to ammonia. 



When water is decomposed by the protoxide of iron in the 

 soil, hydrogen, one of the elements of water, is liberated. Now 

 hydrogen, the instant its liberation is effected, by no means makes 

 its escape a solitary and unattended body, into the atmosphere; 

 but, instead of this, it seizes upon the nhrogen of the air in the 

 soil, and forms ammonia. This in its turn is, or may be fixed by 

 the salts in the soil, or will, under ordinary circumstances, be re- 

 tained for the benefit of the growing crop, even if it is only dis- 

 solved in the water of the soiL 

 11 



