FIXED STATE OF FOOD OF PLANTS IX THE SOIL. 113 



direct proof that plants possess the power of absorbing 

 their necessary nutritive elements from a soil in which 

 they are present in physical combination, i.e. in a 

 state wherein they have lost their solubihty in water ; 

 and the comportment of arable and cultivated soil in 

 general shows that the nutritive substances contained in 

 them must be present in the same form as in the artificial 

 turf soil of these experiments, Avitli this difierence, how- 

 ever, that the earthy particles in the arable soil are not 

 merely the vehicles of these substances, but their source. 

 In a soil consisting of tmf-powder, a second crop will not 

 succeed so well as the first, unless the nutritive sub- 

 stances which have been removed are again supplied ; 

 nor will the soil regain its fertility, however long it be 

 left fallow. 



The benefit derived fi^om mechanical tillage of the 

 ground depends upon the law, that the nutritive substances 

 existing in a fruitful soil are not made to change their 

 place by the water circulating in it ; that the cultivated 

 plants receive their food principally from the earthy 

 particles with which the roots are in direct contact, out 

 of a solution forming around the roots themselves ; and 

 that all nutritive substances Ijang beyond the immediate 

 reach of the roots, though in themselves quite effective as 

 food, are not directly available for the use of the plants. 



There are no isolated laws in nature, but they are 

 all together links in one chain of laws, which are in turn 

 subordinate to a higher and a highest law. 



With the natural law, that organic life is developed 

 only in the outermost crust of the earth which is exposed 

 to the sun, is most intimately connected the power of the 

 fragments of that crust which form the arable surface soil, 

 to collect and retain all those nutritive substances on 

 which life depends. A plant is not, like an animal, 



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