loa THE NEW AGRICULTURE. 



mineral to be presented to the rootlet of a plant as food. How- 

 ever microscopic, it would certainly find obstruction at the 

 point of presentation ; it could not be bodily transported through 

 the cortical covering of the feeding member to be deposited in 

 its integrity as a constituent part of the plant tissue. Such a 

 movement of that part of a soil substance which is of mineral 

 formation could only result in the clogging of the pores, the 

 interruption of the circulation and the consequent death of the 

 plant. 



Upon analysis, however, we do find silica in the mature plant, 

 chiefly in the leaves, so that silica has not only been taken 

 in by the rootlets, but it has been carried by the circulation 

 to those parts most distant from the point of entrance. Since, 

 as we have seen, it is impossible that the particle, as such, 

 should have entered into the plant, it is evident that from its 

 first state outside the plant to its final deposition in the leaf 

 it has undergone a double transformation : first into some sol- 

 uble form in which the member could appropriate it, and then 

 a reconversion into silica on its way along the plant's cir- 

 culation to the place of its final deposition. 



Phosphorus also is an example. In plants, and especially 

 in the seeds of cereals, phosphorus is found for the most part 

 in combination, just as it is in the soil, but in the plant it is 

 the phosphate of potash chiefly, whereas in the soil it is the 

 phosphates of aluminum, iron and lime, showing that the orig- 

 inals in the soil have undergone a complete decomposition 

 and a chemical transformation in the course of their translation 

 to their constituent place in the substance of the plant. 



The dissolving power of water upon many elements of the 

 soil has been referred to in a preceding chapter. When we 

 consider the enormous quantity of water which the growing 



