THE ROOT 93 



upon as food for the plant becomes still narrower : 

 it is reduced to those substances which are soluble in 

 water and acids. 



It would be futile, however, to attempt to grow 

 a plant in artificial soil composed exclusively of nu- 

 trient substances ; for instance, in plant ash. Such 

 soil would be totally unfit for the purpose ; the 

 nutrient substances would be in much too concentrated 

 a form, and the plant would certainly perish. In 

 order to serve the purposes of nutrition, these substances 

 must be mixed and diluted with other inactive matter, 

 such as is found in the insoluble mineral substances of 

 the soil. But if such be the meaning of the latter we 

 can surely substitute for it other substances, less 

 complicated in composition. Indeed, experiment shows 

 that artificial soils can be prepared out of sand, crushed 

 pumice-stone, glass beads, and similar materials. By 

 adding to such foundations the necessary nutrient 

 substances we can obtain very fertile soils. 



We are now within a step of the method for reducing 

 artificial cultures to the simplest form imaginable. If a 

 considerable part of the natural soil as well as the artificial 

 soils just enumerated serve merely for purposes of 

 uniformly distributing and, so to speak, diluting the 

 nutrient substances, would it not be possible to use 

 instead distilled water in which all the nutrient sub- 

 stances necessary to the plant have been dissolved ? 

 Experiments extending over many years, accompanied 

 by many failures, were crowned at last with complete 

 success. To-day, with certain precautions, we can 

 substitute for soil an entirely transparent medium, and 

 grow the most diverse plants in a watery solution, rearing 

 them to the same normal size which they reach in the 

 most fertile soils. 



We take for the purpose a glass jar (fig. 25) containing 

 three or four pounds of distilled water, and dissolve in it 

 something like six or seven grains of a mixture of different 



