Magnesia and Silica 



carbonate. It is not advisable to use lime which 

 contains dolomite on growing crops because the lime 

 carbonates more rapidly than the magnesia, which 

 retains its caustic properties for a long time, and 

 injures the vegetation. 



Sufficient magnesia therefore can be given to the 

 soil without having recourse to any special manure, 

 which would only increase the price of the crops. 



Silica (Si02). 



Silica is found in many plants. Since, however, 

 when consumed it remains entirely unchangeable 

 in the droppings, it can afford no nourishment to 

 plant life. It therefore is not a manure, and it is 

 unnecessary to give it to plants. Its work consists 

 chiefly in giving solidity and hardness, support and 

 protection, to that part of the plants in which it 

 is always found — near the periphery. It is notably 

 present in grasses, and in cereals, where it is found 

 in the stems, the leaves and the husk of the grain, 

 but never in the region of growth or in that 

 reserved for the embryo. It is silica that makes 

 the hard core and hard underskin sometimes found 

 in pears. It does not appear to be necessary for the 

 growth of plants, and if present in any quantity in 

 sugar beet hinders the extraction of the sugar. 



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