1. Bark. 2. Green Layer. 3. Bast. 4. Slippery Layer. 5. Wood. 6. Pith.
“That is what they are for, Tom,” said Uncle George. “Scrape away this green layer. It is greenest on the outside and is rather thick. There are really two or three layers there, but they cannot be separated with a pen-knife. What do you come to next?”
“A white, woody layer with a very slippery surface,” said Frank.
“That slippery surface is itself a layer, and a very important one,” said his uncle. “The wood, you can see, is a very thick layer. In the centre you have a mass of dry, spongy stuff. This is called the pith.”
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.