230 



D. R. Hoagland 



i/> 



JAN. MAR. 



MAY 



JULY SEPT. NOV. JAM. 



Fig. 2. Yields (fresh weights) of shoots and roots of barley plants grown in 

 culture solution, in greenhouse, at different periods of the year; i68 plants grown 

 in each set for periods of approximately 3 weeks. Roots, before weighing, were 

 centrifuged by a uniform technique in order to remove adhering moisture. 



Ca(N03)2 .0025 M 



KNO3 .0025 M 



MgSO* .001 M 



KH2PO4 .0005 M 

 Fe added at intervals as iron tartrate. 



Composition of culture solution: 



pends on suitable illumination, may possibly cause the observed 

 effects on root development. For the particular experiments 

 now under discussion, a simpler explanation cannot at present 

 be excluded, in terms of a supply of organic nutrients, synthe- 

 sized when light of suitable intensity and quality is available, 

 although it does not seem that the problem is one merely of car- 

 bohydrate supply. Whatever the mechanism may be, it is clear 

 that a suggestion emerges for the study of a specific influence 

 of the light factor on root growth and therefore on the relation 

 of the plant to the soil. 



