CONSERVATION OF GROUND WATERS 
191 
falls and from the run-off on its way to the streams. But much 
the greater part of the water used by vegetation must come 
from beneath the surface and must be drawn in by the root 
systems of the plants themselves. During the seasons and periods 
of abundant rainfall, when the groundwater level is high and the 
root systems are laved with moisture, the process of keeping each 
of these miniature waterworks systems in successful operation 
is a relatively simple one. But during dry seasons, when the 
water table has dropped down below the reach of the major 
trunk lines, below even the minor feeders, then the more com- 
, plex operations of capillarity must come into play. 
Capillarity or capillary attraction is the adhesive force by which 
moisture is held in small openings in opposition to the force of 
gravity. This force is sufficient to hold capillary water about 
five feet above the water table in ordinary soils, the actual dis- 
tances ranging from four feet in coarsely sandy soils to eight feet 
in finely sandy or clayey soils (Meyer). It is necessary, of 
course, if life is to be sustained, for connections to be maintained 
between plants, roots, capillary water and gravity water — the 
portion below the water table. I f this connection be broken for 
any extensive period, death must ensue. Because of this fact 
many plants develop root systems several times more extensive 
than that part which is above ground. Thus some of the grasses 
in the western arid regions send their roots down five, six and 
seven feet into the ground in search of moisture, and it has been 
said that alfalfa has been known to grow roots even longer than 
these. The amount of water actually used by plants is probably 
not known, but it must be very great. The amount of transpira- 
tion from the foliage of forest trees ^ — that is, the water which 
passes back into the atmosphere from the pores of the leaves — 
is stated to vary from 1000 to 20,000 pounds per day per acre 
during the growing season, while the transpiration from the leaves 
of maize in the production of a bushel of corn is said to be about 
5000 pounds (Van Hise). It is evident then that great quantities 
of moisture are used by the vegetable life of the land. 
Another important use of ground water is in preserving and 
stabilizing stream flow. While the streams are fed primarily 
by the run-off, their flow is maintained during periods of little 
or no rainfall, which with us includes a majority of the days 
of the year, by springs and by seepage from the rocks and soil. 
The water which escapes in this way and finds its way back to 
