42^ NOURISHMENT OF PLANTS. 



stances thus rendered soluble are taken up by the 

 rain-water, and constitute the salts contained in our 

 common spring and river water. Accordingly, in 

 many places plants receive from water inorganic 

 matter also. 



Finally, the air likewise contains inorganic sub- 

 stances, which have been conveyed into it by evap- 

 oration, especially from the ocean, and also by the 

 force of the winds, and which are diffused by this 

 instrumentality over the whole earth. These are 

 returned again to the earth in rain, dew, snow, etc., 

 and consequently we can no longer be surprised that 

 we often find mineral substances (for instance, com- 

 mon salt, etc.) in plants, which we do not discover 

 in the rocks from which the soil serving as a habi- 

 tation for these vegetables has been derived. 



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Silica, Alumina, Lime, Salts, Humus. 



