THe CARBON DIOXIDE OF THE Sort AIR 337 
Summary of experiment 1 
The results of the first experiment may be summarized as follows: 
1. Soils cropped to oats always contained a greater amount of carbon 
dioxide than did the corresponding bare soils. 
2. The crop hada residual effect, increasing the carbon-dioxide content 
above that in the uncropped soil. 
3. The difference between the amount of carbon dioxide in the cropped 
soil and that in the uncropped soil at the period of most active crop growth, 
divided by the amount of water transpired by the crop, gave an apparent 
constant which varied with the season. 
4. The fact just stated may indicate that the difference between the 
amount of carbon dioxide produced in the cropped soil and that in the 
uncropped soil represented the amount produced by the crop. 
5. It is thus evident that the carbon dioxide from plants and from soil 
organisms accumulated independently. 
6. Fluctuations in the amount of carbon dioxide in the uncropped soil 
were due largely to temperature and pressure variations. High pressures 
produced low contents of carbon dioxide, while high temperatures caused 
high production of carbon dioxide, and vice versa. 
EXPERIMENT 2 
The object of the second experiment was to determine the influence 
of some crop other than oats on the production of carbon dioxide. The 
crop used in this case was common millet (Setaria ttalica). 
Immediately after the harvesting of the 1918 oat crop, millet was planted 
on the same soil and in the same cylinders as were used in experiment 1. 
For experiment 2 the surface layer of sand was entirely removed from 
the soil, which was then thoroly stirred to a depth of about three inches. 
The millet was seeded on four of the soils, of which two had previously 
been in oats and two had been bare. The object in using these two 
different sets was to try to produce some differences in the two crops 
of millet. It was thought that possibly the millet growing on the soil 
which had been previously cropped twice to oats, might not grow well, 
and in such a case a comparison could be made between a good and a 
poor crop of millet. 
