12 EXPERIMENTAL PLANT PHYSIOLOGY 



(6) As the radicle grows the piece of Utmus paper 

 touched by it gradually turns red ; the other strips 

 remain unchanged. 



Inferences. — The root contains an acid which, to 

 some extent, passes from it into the surrounding 

 water. 



As a result of this acid-exudation, the root can absorb, 

 in addition to substances soluble in water, those sub- 

 stances in the soil that will not dissolve in water alone, 

 but are soluble in the acid that the root gives out. 



Growth in Culture Solutions. — It has already been 

 stated (page 1) that the soil is made up of solid particles 

 loosely held together, the spaces between them con- 

 taining air and mineral solutions. 



It is now seen that the plant can feed only on the 

 solutions, since it cannot absorb solid particles however 

 fine they may be. 



In order to determine whether all the soluble sub- 

 stances present in the soil are really necessary to plant- 

 life a series of experiments can be made by growing 

 seedlings in various solutions. Such solutions are 

 termed Culture Solutions; one that contains all the 

 soluble salts commonly found in the soil, in the propor- 

 tion in which they are present, is termed a Normal 

 Culture Solution. Such a solution may be made up as 

 follows : 



1000 c.c. Water made up of Hydrogen and oxygen. 



1 gramme Potassium nitrate „ Potassium, nitrogen, and 



oxygen. 

 •5 „ Calcium sulphate „ Calcium, sulphur, and 



oxygen. 

 •5 „ Magnesium sulphate ,, Magnesium, sulphur, and 



oxygen. 

 •5 „ Calcium phosphate „ Calcium, phosphorus, and 



oxygen. 

 "5 „ Sodium chloride „ Sodium and chlorine. 



A trace Iron sulphate „ Iron, sulphur, and oxygen. 



If the elements in this list are compared with those 

 given in the table of soluble salts in the soil (page 2) 

 it will be seen that they are all included here. 



