jnne, 1920.] SOME SOLUTION CULTURES OF WHEAT 73 



influence. The actual partial concentration of H 2 P0 4 seems to have 

 determined what cultures should give good growth. The suggestion 

 is advanced that this conclusion may not be related to the partial 

 concentration of PO4, but that the controlling feature here encountered 

 may have been the hydrogen-ion concentration (Ph). It is especially 

 important to note that very good solutions for these plants, and for 

 the general conditions of these tests, may be obtained without the use 

 of any potassium at all, if the proper salt proportions are employed. — 

 The three best solutions without potassium had the following volume- 

 molecular partial concentrations of their respective salts : 



(1) Ca(N0 3 ) 2 , 0.00428; Ca(H a POJ^ 0.00214; MgS0 4 , 0.00856. 



(2) Ca(N0 3 ) 2 , 0.00642; Mg(H 2 P0 4 ) 2 , 0.00214; MgS0 4 , 0.00642. 



(3) Ca(NOs) 2l 0.00856; Mg(H 2 P0 4 \, 0.00214; MgS0 4l 0.00428. 

 The value given in each case of course represents the fraction of a 



gram-molecule of the salt contained in a liter of solution. 



Introduction. 



The six essential chemical elements taken up from the soil by 

 ordinary plants (K, Ca, Mg, N, P and S) may be supplied to the roots 

 in the form of aqueous solutions of inorganic salts. Such salt solutions, 

 or "nutrient solutions," offer the very simplest means for supplying 

 those needed elements to growing plants and they are therefore much 

 better suited to the study of the elementary principles of plant phy- 

 siology than are other nutrient media, as sand, soil, etc. The presence 

 of solid particles in the medium complicates the problem enormously 

 and the aqueous solution alone avoids many difficulties of interpreta- 

 tion. For these reasons, many workers have turned to solution cultures 

 as a means for studying the fundamental relations that hold between 

 the plant and its root environment. The preliminary study here re- 

 ported deals with solution cultures of young wheat plants. 



It is often stated, and it is of course obvious to every one, that 

 plants grown with their roots in liquid media alone do not usually 

 develop in exactly the same manner as do plants with their roots 

 surrounded by the two- or three-phase system (solid, liquid, gas) pre- 

 sented by a soil. The ordinary soil solution is of course an aqueous 

 solution of mineral salts and other substances, and if a finely divided 

 and insoluble solid such as quartz is used for experimental cultures, 

 any solution may be added to the dry solid phase, thus avoiding many 

 dissolved compounds that generally exist in soil solutions. But the 



