Oct. IS. I9I9 Relation of Nutrient Medium to Plant Absorption 



85 



was reduced to a more favorable concentration, 

 tion of 3 atmospheres was decidedly injurious. 



An initial concentra- 



Table IV. — Weight, composition, and total absorption per plant 



SAND CULTURES, SERIES 3 



o Averages of 16 plants, except in two highest concentrations in which averages are calculated for eight 

 plants. Mean deviation approximately ± 2 gm. 



The inference from these results is that an optimum concentration and 

 supply of nutrients must be furnished to the plant for perhaps 8 or lo 

 weeks. Burd's (7) investigations have already shown that very little 

 absorption from the soil takes place during the first 3 weeks of growth, 

 so it must follow that the most critical period extends over only 6 or 7 

 weeks. If the nutrient medium is favorable during this period, a very 

 low concentration or small supply may suffice for the remainder of the 

 season, although, as will be proved later, active absorption may continue 

 much longer if suitable solutions are provided. Furthermore, we gain 

 the impression from this experiment that concentrations above 2 atmos- 

 pheres are too great for the barley plant and that the initial stunting is 

 not entirely overcome by a subsequent change to a more favorable 



