6 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
In setting up the first experiment it was thought that in the process of 
aeration a loss of nitrogen from the medium in the form of ammonia might 
occur, especially in view of the fact that the medium was slightly alkaline, 
so that a tube of acid was inserted in the series just beyond each culture 
flask. For this purpose large test tubes, 200x25 mm., and containing 
25 cc. of standardized N/io sulphuric acid were used. As a precaution 
against the backflow of this acid into the cultures, small Erlenmeyer flasks 
of 180 cc. capacity were placed between each culture flask and its corre- 
sponding acid tube. The arrangement of the apparatus can readily be 
understood by consulting text figure i. Two gas-washing bottles, A and B, 
Text Fig. i. Detail of a portion of one of the series of 191 7-1 8. Explanation in 
the text. 
were placed at the head of each series; A contained 30 percent sulphuric 
acid and a quantity of pumice stone; B contained sterilized distilled water. 
Air entered the series through a calcium chloride tube filled with cotton, 
was washed free of ammonia by the acid in A and was moistened by the 
water in B. Oxides of nitrogen would also be removed by the water. 
Before entering the culture flask C the air passed through a second calcium 
chloride tube containing sterilized cotton. The intake tube of each culture 
extended to within an inch or so of the surface of the agar medium, whereas 
the delivery tube merely penetrated the rubber stopper, so that in the process 
of aeration the air above the agar surface was completely changed. After 
leaving the culture flask, the air passed through the safety flask D' and 
bubbled through the acid in the adjoining test tube E'. The intake tube 
of the latter was drawn out to a fine point which extended to the very 
bottom of the test tube, so that only very small bubbles were formed, 
insuring a thorough washing of the air before it passed into the next culture 
flask of the series. The delivery tube of the last acid tube in the series 
was connected to a filter pump, by means of which the air was drawn through 
the whole series at once. 
When the ten series of the first experiment had been completely as- 
