Free water is that form of water which fills our wells, is found in the bottoms of holes dug in the ground during wet seasons and is often found standing on the surface of the soil after heavy or long continued rains. It is sometimes called ground water or standing water and flows under the influence of gravity. Is free water good for the roots of farm plants? If we remember how the root takes its food and moisture, namely through the delicate root hairs; and also remember the experiment which showed us that roots need air, we can readily see that free water would give the root hairs enough moisture, but it would at the same time drown them by cutting off the air. Therefore free water is not directly useful to the roots of house plants or farm plants, excepting such 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).