340 H. W. Turpin 
Fig. 54. MiLLET CROPS SEVEN AND ONE-HALF WEEKS AFTER SEEDING, ON THE TWO SOILS 
HAVING HIGH AND LOW INITIAL CONTENTS OF CARBON DIOXIDE, RESPECTIVELY 
Close view, showing details 
These data are presented diagrammatically in figures 56, 57, and 58, the 
first two representing the data for series 1 and 2, respectively, and the 
third giving these two sets of curves on one sheet. 
It will be noticed that the carbon dioxide in the cropped soils and 
that in the uncropped soils remained the same for the first four weeks 
after seeding. Thereafter the curves for the cropped soils separated 
fairly rapidly from those for the bare soils. In this respect there is no 
difference between the oats and the millet. It will be observed, however, 
that whereas the two oat crops attained their point of maximum carbon- 
dioxide production shortly before heading, the millet crops both gave 
the most carbon dioxide just ten days after heading. In order to bring 
out this point more clearly, curves showing the relationship between the 
amount of carbon dioxide in the oat soil (1917) and that in the millet 
soil (series 2) have been plotted together in figure 59, in such a manner 
that the carbon dioxide produced at the period of heading of each of 
the two crops is on the same ordinate, with the data for a few weeks 
