Uncle George then cut the twig straight across, and the boys saw that each layer formed a ring. In the middle there was a round mass of pith. Around this was a thick ring of wood with the thin slippery layer outside. Outside this was a fairly thick ring, the outer half of which was green in colour. And outside the whole lot was the ring of the thin bark or cork which the boys had first examined. “We have seen,” said Uncle George, “how a one-year-old stem is built. Let us now make a clean cut through the two-year-old part of the twig, and another through the three-year-old part. “You see there are two rings of wood in the two-year-old part and three rings of wood in the three-year-old part. What does this show us?” “That a ring of wood is added every year,” said Frank. “And so, three years ago, this thick branch was a tiny bud,” said Uncle George, pointing to the lower part of the twig. Exercises on Lesson I. 1. An apple will keep sound for months if the skin is unbroken. If we remove a small piece of the skin, the apple soon shrivels up. How is this? 2. Can you explain why we ought not to eat the outer skins of the plum, grape, tomato, pear, etc.? 3. Cut a stout twig of any tree straight through. Make a rough sketch showing the different layers, and tell how old the twig is. 4. Get stout twigs of different trees, such as ash, elm, holly, sycamore. Take about an inch length of each. Split these down the centre, and see if you can make out the different layers on each side of the pith. Make an enlarged drawing of one of these. II.—BULBS AND CORMS. “These,” said Uncle George, “are what we grow our snowdrops and crocuses from.” As he spoke he handed each of the boys a few hard, round objects. Some of these were small, white, and almost pear-shaped. The others were larger, rounder, and brown in colour. “The small white ones are snowdrop _bulbs_,” he continued. “The others are crocus _corms_. There is a great difference between a bulb and a corm, as we shall see when we examine and compare them.” “The corm is covered with brown, papery skins, and has white buds on the top of it,” said Frank. “These brown skins are leaves,” remarked Uncle George. “Leaves?” said Tom. “I thought all leaves were green.” “Oh no, Tom, there are other leaves besides green leaves, called scale-leaves. Green leaves, as you know, give off the moisture which the roots take up from the soil. They also take in plant-food from the air. Scale-leaves protect buds, flowers, and tender stems from cold and from insects. These thin brown leaves of the crocus corm are scale-leaves formed underground. Please remove the brown scale-leaves from one of the corms, Frank.” [Illustration] 1. Snowdrop. 2. Tulip. 3. Narcissus. 4. Crocus.