372 University of California Puhlications in Agricultural Sciences [Vol. 1 



the evidence of a single set of experiments for proof. The evi- 

 dence presented by the work herein reported is an addition to 

 that already reported by other investigators, who have shown 

 that the absorption is influenced to a more or less marked degree 

 by the concentration of the solution. Conclusions which have 

 been reached in regard to the effect of certain variables in this 

 study must be understood to apply only in the case of the specific 

 combinations of salts studied, and in connection with the growth 

 of the tobacco plant in sand cultures. 



The experiments herein reported have in part been made 

 possible by that portion of the Adams fund allotment of the 

 Department of Agriculture of the University of California placed 

 at the disposal of Professor W. A. Setchell of the Department of 

 Botany. It is a pleasure to acknowledge indebtedness to Pro- 

 fessor Charles B. Lipman and to Dr. T. H. Goodspeed, who have 

 by helpful advice and criticism directed the work. 



SUMMARY 



Results are above given which deal with the influence of tht^ 

 composition and concentration of the nutrient solution on sixty 

 dift'erent plants of an F^ species-hybrid of Nicotiana. 



1. 2000 g. of washed sand of known composition was used as 

 a culture medium for each plant. 



2. The salts used were NaNOa, CaCH.POJo, K.SO^, and 

 MgSO,. 



3. The salts were so distributed as to give at least three im- 

 portant variables : first, as to a single nutrient salt ; second, as 

 to total concentration of salts ; and third, as to the balance of 

 salts in the solution. 



4. The influence of the solution on the growth of the plant 

 was judged by the following criteria : height, leaf length, leaf 

 width, flower production, dry weight of tops. 



5. Nitrogen is a more important growth-limiting factor than 

 phosphorus, and phosphorus is, in turn, more important in this 

 capacity than potassium. 



6. The total concentration of the solution has a marked in- 

 fluence upon growth. Plants growing in solutions of low concen- 



