334 H. W. Turpin 4 
by the crop alone. When the carbon dioxide in the uncropped soil was 
subtracted from the carbon dioxide found in the cropped soil, and this 
figure was divided by the amount of water transpired, there resulted 
approximately a constant of 0.024 + .0012 (column G) with a coefficient 
of variability of 22.5 + 3.74 for 1917, and a constant of 0.043 + .0014 
with a coefficient of variability of 15.1 + 2.32 for 1918. When the carbon 
dioxide in the uncropped soil, which may be attributed to bacterial activity, 
was not subtracted (column H), there resulted a constant of 0.042 + .0031 
with a coefficient of variability of 37.4 + 5.65 for 1917, and a constant 
of 0.053 + .0022 with a coefficient of variability of 19.17 + 3.12 for 1918. 
This shows that the constants in the latter cases are not nearly so 
dependable as those in the former, indicating that the carbon dioxide 
produced by the crop is probably the difference between the carbon 
dioxide in the cropped soil and that in the bare soil. That the values 
obtained are not perfect constants can hardly be wondered at when it 
is recalled that the carbon dioxide as determined was not absolute, but 
relative. 
In this connection it may be pointed out that there seems to be some 
ground for concluding that there is a relationship between the water 
transpired by the plant and the carbon-dioxide content of the soil. 
While it is not disputed that the mechanism by which the water is 
actually lost from the leaves of the plant is purely physical and not at 
all associated with vital plant activity, yet the process by which the water 
is brought into the leaves and into a condition to be transpired may well 
be considered as being associated with the life activities of the plant. 
Many investigators have maintained that there is a distinct relationship 
between the life activities of plants and the water transpired. For example, 
as early as 1849 Lawes (1850) considered that the comparative rate of 
transpiration of water to some extent indicated the relative activity of 
the processes of the plant. He drew these conclusions from studies with 
wheat, barley, beans, peas, and clover, in which he compared the amount 
of ash and dry matter obtained from the plants with the water given 
off by them. He found that the larger the amount of dry matter, the 
greater was the quantity of water transpired. These views are supported 
by the investigations of Scrauer (1878, 1880), but the work of Walter 
Wollny (1898) leads to an opposite conelusion. In 1905 Livingston 
(1905) worked with wheat seedlings and concluded that total transpiration 
is as good a criterion for comparing the relative growth of plants in 
