Figure 33 illustrates a simple way to show the value of organic matter in the soil. The boxes are about twelve inches square and ten inches deep. They were filled with a clay subsoil taken from the second foot below the surface of the field. To the second box was added sufficient commercial fertilizer to supply the plants with all necessary plant food. To the third box was added some peat or decayed leaves, in amount about ten per cent. of the clay subsoil. The corn was then planted and the boxes were all given the same care. The better growth of the corn in the third box was due to the fact that the organic matter not only furnished food for the corn but during its decay prepared mineral plant food that was locked up in the clay, and also brought about better conditions of air and moisture by improving the texture of the soil. The plants in the second box had sufficient plant food, but did not make better growth because poor texture prevented proper conditions of air and moisture. "And that's another witness" for organic matter. Decaying organic matter or humus is really the life of the soil and it is greatly needed in most of the farm soils of the eastern part of the country. It closes the pores of sandy soils and opens the clay, thus helping the sand to soak up and hold more moisture and lessening excessive ventilation, and at the same time helping the roots to take a firmer hold. It helps the clay to absorb rain, helps it to pump water faster, helps it to hold water longer in dry weather, increases ventilation, favors root penetration and increases heat absorption. We can increase the amount of organic matter in the soil by plowing in stable manure, leaves and other organic refuse of the farm, or we can plow under crops of clover, grass, grain or other crops grown for that purpose. CHAPTER VIII PLANT FOOD IN THE SOIL We learned in previous paragraphs that the roots of plants take food from the soil, and that a condition necessary for the root to do its work for the plant was the presence of available plant food in sufficient quantities. What is plant food? For answer let us go to the plant and ask it what it is made of. =Experiment.=--Take some newly ripened cotton or cotton wadding, a tree branch, a cornstalk, and some straw or grass. Pull the cotton apart, then twist some of it and pull apart; in turn break the branch, the cornstalk and the straw. The cotton does not pull apart readily nor do the others break easily; this is because they all contain long, tough fibres. These fibres are called woody fibre or cellulose. The cotton fibre is nearly pure cellulose.