Oct. IS. 1919 Relation of Nutrient Medium to Plant A bsorption 8 1 



SAND CULTURES, SERIES 2 



In any experiment similar to the one first described, it is clearly 

 unjustifiable to interpret the results in terms of concentration or ionic 

 ratios. Such an interpretation is warranted only when an opportunity 

 is afforded for controlling the concentration of the solution at all times. 

 In this second experiment the method of McCall {26) has been adopted, 

 as previously stated. Solutions were changed during the period of 

 active absorption every three days ; and observations on the sand showed 

 that the solutions were kept relatively constant, although on some 

 occasions the leaching of nutrients to the bottom of the jar caused con- 

 siderable fluctuations. 



The plants Vvcre grown out of doors from August to December. There 

 was abundant vegetative growth, but the temperature and light condi- 

 tions did not permit the production of grain. The plants Vv^ere still 

 green when cut. We may use the data from this experiment, therefore, 

 to indicate the general relation of concentration to yield in terms of 

 dry weight of tops and roots and to the absorption of important ele- 

 ments while the plant is in an active state of metabolism. 



The composition of the nutrient solution used in this and subsequent 

 experiments had its basis in the analyses of water extracts of soils which 

 had been under observation for several years, as described by Stewart {42) . 

 The nutrient solution was so constituted as to give approximately the 

 same relations between the more important ions as that found in the 

 water extracts of fertile soils at the period when the crop was actively 

 absorbing. For the purposes of the present investigation this seemed as 

 logical a basis as any for making up the nutrient solution. Possibly other 

 combinations might give somewhat higher yields at times, but the ratios 

 between the elements in the solutions employed were certainly not 

 unfavorable. Moreover, within wide limits the broad relations of reac- 

 tion and concentration to the course of absorption will not be affected 

 by small differences in ionic ratios. 



The nutrient solution of 0.78 atmospheres osmotic pressure had the 

 following composition : 



p. p. m. 



NO3 700 



K 284 



PO, 136 



Ca ^ 200 



Mg 99 



SO4 368 



NaCl 30 



Ph=6.8. 



The other concentrations used were o.io, 0.25, 0.48, and 1.45 atmos- 

 pheres. 



The yields and analyses of plants are given in Table III. 



