562 AMERICAN JOURNAL OF BOTANY [Vol. 10, 
As is indicated by the lack of agreement between corresponding ratio 
values, there is a marked difference between the plants grown in the simple 
solution cultures and those grown in the simple aerated solution cultures 
with respect to the distribution of total yield values among the various 
plant parts (stems, leaves, fruit, and roots). Corresponding ratio values 
relating to the drip cultures and the aerated-drip cultures, however, show 
fairly close agreement, thus indicating that the development of the plant 
parts relative to the total yields produced is similar under these experimen¬ 
tal treatments but is quite different in this respect from the development 
of the plant parts in the simple cultures and the simple aerated cultures. A 
comparison of the corresponding data of tables 2 and 4 brings out the fact 
that this relation of average partial yields (stems, leaves, etc.) to average 
total yields of the plants grown in the drip-solution cultures, both aerated 
and non-aerated, is quite in agreement with that shown for the plants grown 
in the sand cultures under the various experimental treatments. It is 
interesting here to note also that the average total yields obtained from the 
sand cultures were throughout uniformly much higher than were those 
obtained from the solution cultures. 
Oxygen Relations 
Quantitative determinations of the dissolved oxygen content of the 
culture solutions were made at the time of solution renewal of those cultures 
not receiving constant drip after the solutions had been in contact with the 
plant roots for a period of three and one half days. No oxygen determina¬ 
tions were made upon the solutions in the sand cultures owing to the diffi¬ 
culty of collecting solution samples from these cultures without undue 
exposure to the atmosphere, which, of course, would have rendered tests 
upon such samples worthless in so far as they could have represented the 
true oxygen content of the solutions in contact with the plant roots at the 
time of sampling. The micro-Winkler method proposed by Lund (3) was 
used in making all the determinations. 
From a large number of oxygen determinations, the results of those made 
during the second, fourth, sixth, and eighth weeks of the growth period are 
given in table 5 in terms of parts per million. These values are represen¬ 
tative and show the general effect of the plants upon the solutions with re¬ 
spect to the supply of dissolved oxygen under the various experimental 
treatments and at different stages of the development of the plants. 
From the data of table 5 it will be observed that after the second week of 
the growth period the oxygen content of the solutions not aerated was 
nearly exhausted by the plants during a three and one half day period. The 
oxygen content of the solutions which were continuously renewed but not 
aerated was also greatly reduced. This indicates that a constant drip by 
which one liter of fresh solution is supplied during each 24-hour period does 
not keep up the oxygen supply of the cultures which is necessary for maxi- 
