Dec., 1923] 
ALLISON AND SHIVE-GROWTH OF SOYBEANS 
563 
Table 5. Effect of Soybean Plants upon the Oxygen Content of the 
Nutrient Solutions under the Various Experimental Conditions 
Cultures 
Oxygen Content (p.p.m.)* 
2nd week 
4th week 
6th week 
8th week 
Simple solution. 
475 
1.25 
1.00 
175 
Simple aerated solution. 
7.00 
6-75 
7.50 
8.00 
Drip solution. 
6.95 
375 
2-95 
3.00 
Aerated-drip solution. 
7.20 
6-95 
5.85 
6.00 
* The initial oxygen content of the solutions was approximately 8.1 p.p.m. at green¬ 
house temperature. 
mum development of the plants. On the other hand, the data show that 
the oxygen content of the aerated solutions was maintained at a relatively 
high level, but even in these solutions the action of the plants reduced the 
oxygen pressure so that it was always slightly below the initial pressure al¬ 
though the solutions were vigorously and continuously aerated. 
It has already been pointed out that maintaining the oxygen supply of 
the nutrient solutions through aeration has no beneficial influence upon the 
growth of the plant tops and only slightly increases the root yields when 
grown in the nutrient solutions which were only intermittently renewed. 
This is in accord with Pember’s (5) report that barley did not respond to 
aeration when grown in solutions which were renewed every two weeks. 
Free (2) likewise has reported that buckwheat showed no response to aera¬ 
tion when grown in solution cultures with intermittent solution renewal. 
On the other hand, the data of tables 1 and 3 show that the maintenance, 
through vigorous aeration, of a high content of dissolved oxygen in the 
culture solutions which were continuously renewed had a very pronounced 
effect upon the manner of growth (especially with reference to the roots) 
and upon the final yields of soybeans. The average total yield from the 
aerated-drip sand cultures was 26 percent higher than the corresponding 
yield from the drip sand cultures without aeration. Likewise, the continu¬ 
ously renewed solution cultures with aeration produced an average total 
yield 49 percent above the corresponding yield from the drip-solution cul¬ 
tures without aeration. As previously stated, the solutions of all these 
cultures were renewed by a constant drip at the rate of one liter per culture 
in twenty-four hours. Whether or not a higher rate of solution flow could 
influence the final yields has not been tested. 
H-ion Concentration Relations 
An important consideration to which little attention has as yet been 
given is the relation of the change of hydrogen-ion concentration in culture 
solutions under various experimental conditions to the development of the 
plants. While the cause of this well defined reaction change resulting from 
