Part 2

“Very good,” said Uncle George. “That is exactly what I wanted you to notice. The swollen parts of a stem are called its nodes. In every stem, buds and leaves occur at the nodes. Nodes are very well seen in grass and corn stems.”

“Then at the top of the twig there is a very large bud and a pair of small buds, one on each side of it,” said Frank.

“You have described it very well,” said his uncle. “Now, Tom, what about the willow twig?”

“I see some very tiny marks on it,” said Tom. “There are no rings marking the year’s growth; and the buds are not arranged in pairs.”

“That is quite right, Tom. Willow grows very quickly. Your twig is all one season’s growth. It is smooth and green—not brown like the horse-chestnut twig. The buds are arranged alternately. That is to say, there is only one bud at each node.”

“Now, let us see what the horse-chestnut twig is made of.”

Uncle George next cut two pieces off the top part of the horse-chestnut twig and handed one to each of the boys.

“Now, take your knives,” he said, “and carefully peel off a very small piece of the brown covering. You will have to be very careful, as it is very thin and rather difficult to remove. Ah, Frank, you have done that very nicely. Now, hold it up to the light and tell us what you think it is for.”

“It is the skin or covering of the twig,” said Frank.

“It is; and if you look with your lens you will see that the tiny markings on it are holes. It is really a thin layer of bark or cork. Perhaps you can tell me why the twig is covered with a thin layer of cork?”

“To keep water from getting in,” said Frank.

“Rather to keep water from getting out,” said Uncle George. “You must remember that water is continually passing up stems from the roots. Water cannot pass through cork. If we were to remove the cork layer from the outside of a growing twig, that twig would shrivel up and die. There is also a layer of cork protecting the willow twig, but it is so very thin that we can see through it. Remove as much of the cork layer as you can, and tell me what is underneath.”

“There is a layer of green stuff beneath,” said Frank.

“Just so,” said Uncle George. “Now, if you remember, I once told you that plants took most of their food from the air by means of the green stuff in their leaves. This green layer in the twig does the same thing; but how can the air get in if it is covered up by a layer of cork?”

“Oh, I see now,” said Tom, “what the tiny holes or pits are for—to let air in to the green layer underneath.”

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.

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.”