98 



Journal of Agricultural Research voi. xvm. no. 



Table X. — Yields of tops and roots 



WATER CULTURES, SERIES 4 

 [Plants grown for eight weeks] 



The yields from concentrations of 0.07 atmospheres and 1.70 atmos- 

 pheres are decidedly inferior to those from concentrations of 0.58 atmos- 

 pheres and 0.90 atmospheres. Between the two latter there is no 

 significant difference. The yields of plants from the acid solution are at 

 least equal and possibly superior to those from the neutral solution. 

 Certainly there is no evidence of inhibition in the acid solutions, except 

 with the highest concentration. This is a super-optimum concentration for 

 both acid and neutral solutions; but in the acid solution of this highest 

 concentration the roots were distinctly injured, while those in the 

 corresponding neutral solution had a more normal appearance. In the 

 other solutions of similar hydrogen-ion concentration the roots were quite 

 uninjured. In other words, the injury referred to was the resultant 

 effect of the hydrogen-ion concentration and super-optimum total con- 

 centration, or more specifically, perhaps, due to the high concentration 

 of PO4 in the acid solution. A much larger quantity of PO4 was ab- 

 sorbed in the latter case. 



It should be emphasized in connection with the relative yields that 

 the most dilute solution was exhausted of its NO3 in less than 72 hours. 

 The question then arises, whether the diminution in yield might not be 

 due to a deficiency in total quantity of one or more ions rather than to 

 sub-optimum concentration. 



This suggestion led to a further water-culture experiment, series 5. 

 Twenty plants were grown in bottles of 2,200-cc. capacity with only i 

 plant in each bottle. Solutions were changed, after the first few weeks, 

 about five times each week. In this way, as analysis showed, the solu- 

 tions were maintained practically constant. The composition of the 

 solutions was similar to that described before, two concentrations being 

 used of 0.07 atmospheres and 0.58 atmospheres. After seven weeks the 

 plants were cut and weighed in the air-dry state. The concentration of 

 0.07 atmospheres gave a yield of 0.60 ±0.08 gm. of tops and 0.20 gm. of 



