Transpiration as a Factor in Crop Production. 
17 
duced the amount of water transpired per gram of ash content 
38 per cent, and per gram of dry matter 40.5 per cent. 
A natural climatic difference which lowered the free water 
surface evaporation 40 per cent during July and August in 1913, 
as compared with 1914, reduced the transpiration per gram of 
ash content 22 per cent and per gram of dry matter 27 per cent. 
The greater the availability of the soil solutes in different 
degrees of soil fertility, other conditions being equal, (1) the 
greater was the amount of solute taken in per unit of water 
transpired, (2) the greater was the dry matter produced, (3) 
the greater was the total amount of water transpired, (4) the 
greater was the total amount of solute taken into the plant, and 
(5) the smaller was the amount of water used per unit of dry 
matter. 
Less water was transpired per gram of ash content and also 
per gram of dry matter in a relatively low soil saturation than 
where an abundance of water was present. 
The size of the potometer and consequent degree of soil limita- 
tion exerts a great influence upon the relation of transpiration 
to the intake of soil solutes. The quantity of transpiration per 
gram of ash content decreases rather consistently as the size of 
the potometer and amount of soil increases. In potometers con- 
taining 32.5, 85, 150, 239, 583, and 956 pounds of soil, the amount 
of transpiration per gram of ash content was: 6.14, 5.70, 5.20, 
5.50, 5.07, and 4.32 kilograms, respectively. 
Considerable variation exists in the ash and transpiration re- 
lationships of different corn varieties, but there appears to be no 
absolute correlation between the percentage of ash, the quantity 
of water transpired per gram of ash content, or the transpiration 
per gram of dry matter. There is, however, a strong tendency 
for varieties having a low water requirement per gram of dry 
matter, to have also a relatively low transpiration rate per gram 
of ash content. Milo and Black Amber sorghum transpired a 
slightly smaller quantity of water per gram of ash content than 
the average for the corn, while sunflowers transpired relatively 
much more per gram of ash content. 
From a review of all of the data it may be concluded that at 
least within the practical limits of crop production, other things 
being equal, an increase in the density of the soil solution is 
accompanied by an increase in the amount of solute taken into 
the plant per unit of water transpired. Such a relationship is 
subject to climatic influences. Plants growing in a weak soil 
solution as exists in a soil of low fertility, under conditions of 
low evaporation, may take in a larger amount of solutes per 
unit of water transpired than would be the case in a stronger 
