AnpREWs & BEALS: GROWTH OF ZEA MAYS 95 
without further attention. The Kekulé apparatus as described 
by Ostwald is very convenient for aération. The glass tube ex- 
tends to near the bottom of the cylinder to aérate the solution as 
perfectly as possible. The resistance can be varied by raising 
and lowering the tube in the cylinder, and the opening of the tube is 
slightly contracted to form smaller air bubbles. Care, however, 
must be used or the resistance will be so great that the water , 
pressure will not force the air bubbles through with sufficient 
rapidity. 
The Bunsen filter pump affords a greater quantity of air than 
the Kekulé apparatus. From the Bunsen filter pump apparatus 
numerous lateral tubes can be attached to a main air pipe leading 
from the pump so that fifteen to twenty cultures can be aérated 
at once. The supply of air to the individual water cultures is 
regulated by pinch cocks on the connecting rubber tubes and by 
raising or lowering these in the solutions. 
A short paper appeared by Free* on the aération of buckwheat, 
in 1917, in which it was found “ that the degree of aeration of the 
culture solution is without important influence.’ Stiles and 
Jorgensen} obtained the same result with buckwheat as Free. 
As the columns of air carried down the tube are much larger 
and of much greater volume than the drops of water, it was found 
upon measurement that 3.5 times as much air was passed through 
the solution by the Kekulé apparatus as the volume of water 
required to convey the air. About 100 c.c. of air were passed 
through the solution per minute. 
TABLE VI 
Number of days Aérated Non-aérated 
2 25-0 19°C 
3 ee rt ee 
6 DEG i ie 
8 seo * 23.0" 
ha * 23.0; <* a4.0°° 0 
15 a0 33.0 
20 47.0 “ 37.0 * 
26 65.0" 7 46.0 “ 
r-cultures. Johns 

* The effect of aeration on the growth of buckwheat in wate 
Hopkins Univ. Cire. 293: 198, 199. I917- 
+ Observations on the influence of aeration of the nutrient solution in water 
culture experiments, with some remarks on the water culture method. New Phytol. 
16: 181-197. 1917. ; 
