If the tree be girdled the roots sooner or later suffer from lack of food supply from the leaves. Owing to this food stoppage the roots will cease to grow and will soon be unable to take in sufficient water, and then the leaves will begin to droop. This, however, may not happen until several months after the girdling. Sometimes a partly girdled branch grows much in thickness just above the girdle, as is shown in Fig. 29. This extra growth seems to be due to a stoppage of the rich supply of food which was on its way to the roots through the bark. It could go no farther and was therefore used by the tree to make an unnatural growth at this point. You will now understand how and why trees die when they are girdled to clear new ground. [Illustration: FIG. 29. A THICKENING ABOVE THE WIRE THAT CAUSED THE GIRDLING] It is, then, the general law of sap-movement that the upward current from the roots passes through the woody portion of the trunk, and that the current bearing the food made by the leaves passes downward through the bark. =EXERCISE= Let the teacher see that these and all other experiments are performed by the pupils. Do not allow them to guess, but make them see. Girdle valueless trees or saplings of several kinds, cutting the bark away in a complete circle around the tree. Do not cut into the wood. How long before the tree shows signs of injury? Girdle a single small limb on a tree. What happens? Explain. SECTION XIV. THE FLOWER AND THE SEED Some people think that the flowers by the wayside are for the purpose of beautifying the world and increasing man's enjoyment. Do you think this is true? Undoubtedly a flower is beautiful, and to be beautiful is one of the uses of many flowers; but it is not the chief use of a flower. You know that when peach or apple blossoms are nipped by the spring frost the fruit crop is in danger. The fruit of the plant bears the seed, and the flower produces the fruit. That is its chief duty. [Illustration: FIG. 30. PARTS OF THE PISTIL] Do you know any plant that produces seed without flowers? Some one answers, "The corn, the elm, and the maple all produce seed, but have no flower." No, that is not correct. If you look closely you will find in the spring very small flowers on the elm and on the maple, while the ear and the tassel are really the blossoms of the corn plant. Every plant that produces seed has flowers, although they may sometimes seem very curious flowers. [Illustration: FIG. 31. A BUTTERCUP]