Relation of Xonavailable Water to Hygroscopic Coefficient 117 
muck below tke wilting coefficient wkile tkat of tke lower portion, 
wkere the roots, altko muck less abundant, were still present, was 
muck above tke wilting coefficient. Tkis would indicate tkat 
wken once tke roots are developed in tke subsoil tkey fail to dis- 
tinguisk skarply between tke portion of tke free water above tke 
wilting coefficient and tke portion below; otkerwise, after tke 
moisture in a portion of tke subsoil kad been reduced to tke wilt- 
ing coefficient, water removal from tkis portion would cease so 
long as roots of tke same plant were in contact witk subsoil with 
a moisture content above tke wilting coefficient. It seems tkat in 
reality tke roots in tke drier portions of tke subsoil may be re- 
moving u water nonavailable for growtk" at tke same time tkat 
roots of tke same plant in moist subsoil are removing "water 
available for growtk," 
Even if tke soil moisture supply is so low tkat no growtk can 
take place, it may suffice for tke maturing of some seed, as witk 
a wkeat crop, or for tke maintenance of life in tke case of per- 
ennials. Witk tke latter tke mere maintenance of life tkru a 
very dry period may be far more important tkan any growtk in 
tkat particular year, as in tke case of orckards, kedges, and even 
alfalfa fields. A sligkt difference in tke ability of a perennial 
plant to make use of tke last portion of tke free water may deter- 
mine wketker or not it is adapted to extremely severe conditions. 
As an illustration of tke relative value of tke two coefficients 
in comparisons of available moisture in field studies tke data in 
Tables 33 to 36 are presented. Tke field referred to in Table 
33 is on tke farm of Hon. George Coupland near Elgin, Nebraska. 
It kad been in alfalfa for ten years and at tke time of sampling 
tkere was still a fair stand of kealtky plants. Tke water-table 
was probably at a deptk of 45 to 50 feet below tke surface of 
tke field, tke soil of wkick consists of loess to a deptk of 35 feet. 
Tke alfalfa field referred to in Table 34 is adjacent to tke Ne- 
braska Experiment Station farm. It kad been in alfalfa for 
five or six years and, judging from its vigorous growtk during 
prolonged droutks, tke alfalfa plants derived muck water from 
tke water-table, wkick at tke time of sampling was between 11 
and 12 feet below tke surface. Tke locust grove (Table 35) is on 
tke H O Ranck near Madrid, in western Nebraska. At tke time 
tke samples were taken it kad passed tkru a droutk remarkable 
botk for its duration and for its severity. All tke trees, altko 
not in leaf at tke time, were alive, as evidenced by tbeir still being 
alive a year later. Tke abandoned olive orckard referred to in 
Table 36 is near Casa Grande, Arizona, and kas been described by 
Mason. 1 Tke s amples were taken by tke writer from a trenck 
1 Mason, S. C. Drought Resistance of the Olive in the Southwestern 
States. Bui. 192, Bureau of Plant Industry, U. S. Dept. of Agriculture 
1911, p. 13. 
