THE ROOT 



97 



the fourth no potassium nor phosphoric acid. The 

 results speak for themselves. 



Here is one more experiment, the most obvious and 



FIG. 27. 



striking of all in its results. Among the salts" found to 

 be indispensable for the nutrition of the plant, there 

 stands that of iron ; it enters into the composition of 

 the ash of the plant in very minute quantities. This 

 salt cannot be used as a solution in water cultures, 



G 



