Dec., 1923] 
ALLISON AND SHIVE-GROWTH OF SOYBEANS 
565 
change diminishes gradually with approaching maturity of the plants, as the 
graph shows. This graph represents the usual trend of reaction change 
produced by normal soybean plants in these three-salt solutions. How¬ 
ever, it will be observed from a comparison of this graph with that repre¬ 
senting the pH values of the solutions of the non-drip cultures that a con¬ 
stant drip which supplied one liter of new solution to a culture during a 
twenty-four hour period considerably retarded reaction change but is by 
no means an effective method of controlling this influence of the plants upon 
the medium. 
The graph representing the pH values of the non-drip cultures is mar¬ 
kedly divergent from that representing the pH values of the drip cultures, 
the former having reached a maximum reaction change considerably greater 
than that of the latter and occurring two weeks earlier. It is quite prob¬ 
able that this pronounced and rapid reaction change in the solutions of the 
non-drip cultures during the very early stages of growth may result in re¬ 
tarded plant activity during subsequent development. Such retarded 
activity is actually shown for the plants of the non-drip cultures following 
the third week of the growth period, if the relative rates of reaction change 
produced by the plants may be taken as an index. This is clearly indi¬ 
cated by the marked decline in the graph of pH values for these cultures 
during the fourth, fifth, and sixth weeks. It is to be noted also that the 
growth of the plants of these cultures was abnormal, showing thick and 
brittle leaves and very thick and highly pubescent stems, somewhat like 
the abnormal stem growth of soybean plants described by McCall (4). 
This was found to be particularly noticeable in the aerated-non-drip cul¬ 
tures. The plants of the non-drip cultures were also considerably later 
in maturing seed than were those of the drip cultures. Seeds from the 
drip cultures were tested for germination and were found to germinate well 
and to produce normal seedlings. .Seeds from the non-drip cultures, on 
the other hand, were neither so well developed nor so mature as were those 
from the drip cultures. 
Summary 
This paper presents the results of a preliminary study of aeration and 
continuous renewal of nutrient culture solution as related to the growth of 
soybeans in solution and sand cultures. Some of the main points to be 
emphasized in a tentative way may be summarized as follows: 
1. Solution or sand cultures with continuous solution renewal by which 
one liter of new solution per culture was supplied during each 24-hour 
interval throughout the growth period always produced plants which were 
superior in every respect to those grown in cultures with intermittent solu¬ 
tion renewal. However, the best plants with respect to health, vigor, and 
yields always occurred in the cultures with continuous solution renewal and 
with constant and thorough aeration of the medium. 
2. Aeration of solution or sand cultures which maintained the maximum 
supply of dissolved oxygen (approximate saturation) in the culture solu- 
