Relation of Nonavailable Water to Hygroscopic Coefficient 121 
crop plants niay die quickly if conditions are such as to cause 
an unusually rapid transpiration. An abundance of free water 
in deeper portions of the subsoil, into which but few roots have 
been dev eloped, may not avail to carry the plant over such a 
critical period. 
The economy in the use of a certain amount of free water 
stored in the subsoil may be much affected by its distribution. A 
high content confined to the portion of the soil near the surface 
may induce a rapid growth of the plants and an economical use 
of the water in so far as the production of foliage alone is con- 
cerned, but the resulting large transpiring surface may cause the 
death of the plants before they reach maturity. The same 
amount of free water distributed thru a greater depth may in- 
duce a slower growth, allow a longer lease of life, and so permit 
of the production of seed, while if the same amount be distributed 
thru a still greater depth the content of free water may every- 
where be too low to permit of the development of roots, thus ren- 
dering the free water nonavailable. 
The loss of water from the subsoil of dry lands under crop 
seems to take place almost entirely thru transpiration. In the 
absence of plants the loss from the subsoil is small. The stored 
moisture of the different depths of subsoil in the field becomes 
available to the plants by the roots being developed into these 
depths, but little moisture being elevated to the roots by capil- 
larity. However, in the case of subsoils saturated in cylinders 
or pots and comparable to such field subsoils as are only a few 
feet above the water-table, the content of free water is so high 
that large amounts of moisture may be elevated to the roots by 
capillarity. The amount of water retained by a soil saturated in 
pots or cylinders is far in excess of the amount retained by a 
similar soil saturated in a field where the water-table is at a 
considerable depth below the surface, as in ordinary dry-land 
soils. 
To obtain a basis for comparing the available moisture in 
soils, either the hygroscopic coefficient or the wilting coefficient 
may be used. In general the one may prove as satisfactory as 
the other, but in considering the germination of seeds and the 
development of roots, and hence the whole of the earlier portion 
of the life of annual crop plants, the wilting coefficient appears 
the preferable; while in considering the production of seed in 
the case of annual crop plants, and the maintenance of life and 
even the growth of perennial plants, the hygroscopic coefficient 
appears much the preferable. 
In the case of ordinary dry-land soils, the water-table being 
at a considerable depth below the surface, the maximum amount 
