THE WILTING COEFFICIENT AND ITS INDIRECT 
DETERMINATION’ 
LyMAN J. Briccs anp H. L. SHANTZ 
THE WILTING COEFFICIENT 
If the roots of a plant are well established in a mass of soil, the 
plant gradually reduces the water content until permanent wilting 
occurs. The water remaining in the soil under this condition has 
been termed non-available by previous writers. We have found, 
however, that plants can reduce the soil moisture content somewhat 
below the point corresponding to the permanent wilting of the 
leaves, so that the water content at the wilting point is not strictly 
non-available. In fact, this loss of water from the soil to the air 
goes on through the plant tissues even after the death of the plant, 
and appears to be limited only by the establishment of a state of 
equilibrium between the soil and the air. The plant during the 
drying stage acts simply as a medium for the transference of water, 
and while the rate of loss is reduced, the final result is the same as 
if the air and soil were in direct contact. By means of the wax 
seal method, which effectually prevents all direct loss of water from 
the soil, we have been able to demonstrate conclusively that there 
is a continued loss of water from the soil through the plant long 
after wilting occurs. This is shown by the results given in the 
accompanying table (table I). 
The wheat seedlings were grown in sealed glass pots containing 
about 200 grams of soil. The second column of the table gives the 
water content of the soil corresponding to the wilting of the plants. 
The third column gives the number of days intervening between the 
wilting and the death of the plants, at which time the moisture 
content of the soil had been materially reduced, as shown in the 
fourth column. A still greater loss of water occurred during the 
subsequent period, at the end of which the moisture content of the 
* Published by permission of the Secretary of Agriculture. 
Botanical Gazette, vol. 53] [20 
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