Transpiration as a Factor in Crop Production. 
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Chart VII. — Effect of size of potometer upon the amount of water required 
to produce one gram total dry matter with corn. 1914. See Table 7. 
EFFECT OF EXPOSURE OF POTOMETER ON THE GROWTH AND 
WATER REQUIREMENTS OF CORN. 1 
As is rather customary in pot experiments, our potometers 
have been exposed to the surrounding atmospheric conditions 
rather than buried in the soil. This greatly facilitates weighing 
and handling, but subjects the soil contents to somewhat different 
temperatures than are normal under field conditions. Potom- 
eters exposed in this manner have been criticized by several 
investigators. Fortier, Hasselbring, Thorn, and Willard and 
Humbert have surrounded their pots with a water jacket, for 
the purpose of reducing temperature fluctuations. In order to 
secure data concerning the effect of this exposure upon soil temper- 
ature, growth, and transpiration, the tests reported in Tables 
9, 10, and 11 were made. 
The subirrigation type of potometer was used and all were 
filled with fertile surface-loam soil equivalent to 239 pounds 
moisture-free soil, and 1.75 pounds moisture-free sheep manure 
was added. Eight potometers were fully exposed in the pit, and 
eight were buried in the soil in the field and connected by means of 
1 References concerning the effect of the exposure of the potometer: 
King (1895), Leather (1911), Liebscher (1895), and Briggs and Shantz (1914) 
