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in water ; and this power we find in the vitality of 

 plants. 



The delicate fibres-ofthe roots consist of a number 

 of minute cells which press against the surrounding 

 soil. The contents of these cells, the sap, is divided 

 from the particles of earth enclosing it by a thin 

 permeable membrane only, and, contact being 

 established by the moisture in the soil, " Endos- 

 mose" comes into play. This is the power which 

 overcomes the physical force of attraction ; the 

 mineral plant-food, being thus restored to its 

 previous state of solubility in water, permeates 

 through the thin membrane of the root-cells, and 

 enters the system of the plant. 



Now, to judge correctly of the capabilities of a soil, 

 we have to distinguish into two great classes those of 

 its constituent parts which serve as food for plants. 

 The first includes all those minerals which, by the 

 disintegrating action of moisture, heat, and atmos- 

 pheric air, have been converted into a state of solu- 

 bility in water, and are retained in physical combi- 

 nation with the soil xmly by the slight force of, what 

 has been termed, its capillary attractive power. To 

 the second class belong all those constituents which 

 are still in a state of chemical combination ; as, in- 

 soluble silicates of potassa, phosphates of lime, &c. 



The first of these classes is most important if we 

 regard the immediate wants of agriculture ; it is this 

 portion which we have chiefly to consider when the 



