When the hot, dry days of summer come, the soil depends upon the subsoil, or undersoil, for the moisture that it must furnish its growing plants. The water was stored in the soil during the fall, winter, and spring months when there was plenty of rain. If you dig down into the soil when everything is dry and hot, you will soon reach a cool, moist undersoil. The moisture increases as you dig deeper into the soil. Now the roots of plants go down into the soil for this moisture, because they need the water to carry the plant food up into the stems and leaves. You can see how the water rises in the soil by performing a simple experiment. =EXPERIMENT= Take a lamp-chimney and fill it with fine, dry dirt. The dirt from a road or a field will do. Tie over the smaller end of the lamp-chimney a piece of cloth or a pocket handkerchief, and place this end in a shallow pan of water. If the soil in the lamp-chimney is clay and well packed, the water will quickly rise to the top. By filling three or four lamp-chimneys with as many different soils, the pupil will see that the water rises more slowly in some than in others. Now take the water pan away, and the water in the lamp-chimneys will gradually evaporate. Study for a few days the effect of evaporation on the several soils. SECTION V. DRAINING THE SOIL A wise man was once asked, "What is the most valuable improvement ever made in agriculture?" He answered, "Drainage." Often soils unfit for crop-production because they contain too much water are by drainage rendered the most valuable of farming lands. Drainage benefits land in the following ways: 1. It deepens the subsoil by removing unnecessary water from the spaces between the soil particles. This admits air. Then the oxygen which is in the air, by aiding decay, prepares plant food for vegetation. 2. It makes the surface soil, or topsoil, deeper. It stands to reason that the deeper the soil the more plant food becomes available for plant use. 3. It improves the texture of the soil. Wet soil is sticky. Drainage makes this sticky soil crumble and fall apart. 4. It prevents washing. 5. It increases the porosity of soils and permits roots to go deeper into the soil for food and moisture. 6. It increases the warmth of the soil. 7. It permits earlier working in spring and after rains. [Illustration: FIG. 9. LAYING A TILE DRAIN] 8. It favors the growth of germs which change the unavailable nitrogen of the soil into nitrates; that is, into the form of nitrogen most useful to plants. 9. It enables plants to resist drought better because the roots go into the ground deeper early in the season. A soil that is hard and wet will not grow good crops. The nitrogen-gathering crops will store the greatest quantity of nitrogen in the soil when the soil is open to the free circulation of the air. These valuable crops cannot do this when the soil is wet and cold.