as are naturally
swamp plants, like rice, which grows part of the time with its
roots covered with free water.

[Illustration: FIG. 26.--CAPILLARY TUBES.
To show how water rises in small tubes or is drawn into small spaces.]

[Illustration: FIG. 27.--CAPILLARY PLATES.
Water is drawn to the highest point where the glass plates are closest
together.]

[Illustration: FIG. 28.
A cone of soil to show capillarity. Water poured about the base of
this cone of soil has been drawn by capillary force half-way to the
top.]

[Illustration: FIG. 29.
To show the relative amounts of film-moisture held by coarse and fine
soils. The colored water in bottle _A_ represents the amount of water
required to cover the half pound of pebbles in the tumbler _B_ with a
film of moisture. The colored water in bottle _C_ shows the amount
required to cover the soil grains in the half pound of sand in tumbler
_D._]

CAPILLARY WATER

If you will take a number of glass tubes of different sizes, the
largest not more than one-fourth of an inch in diameter, and hold them
with one end of each in water or some colored liquid, you will notice
that the water rises in the tubes (Fig. 26), and that it rises highest
in the smallest tube. The force which causes the water to rise in
these tubes is called the capillary force, from the old Latin word
_capillum_ (a hair), because it is most marked in hair-like tubes, the
smaller the tube the higher the water will rise. The water which rises
in the tubes is called capillary water.

Another method of illustrating capillary water is to tie or hold
together two flat pieces of glass, keeping two of the edges close
together and separating the opposite two about one-eighth of an inch
with a sliver of wood. Then set them in a plate of water or colored
liquid and notice how the water rises between the pieces of glass,
rising higher the smaller the space (Fig. 27). It is the capillary
force which causes water to rise in a piece of cloth or paper dipped
in water.

Take a plate and pour onto it a cone-shaped pile of dry sand or fine
soil; then pour water around the base of the pile and note how the
water is drawn up into the soil by capillary force (Fig. 28).

Capillary water is the other important form of water in the soil. This
is moisture which is drawn by capillary force or soaks into the spaces
between the soil particles and covers each particle with a thin film
of moisture.

FILM WATER

Take a marble o