Trunks of trees.
We speak of plants as having stalks, and of trees as having trunks. A tree has a stout firm trunk, because its top is so large and heavy. Its branches spread out so much, that the tree would be broken down by the wind if it did not have a strong trunk.
It is the woody part of the trunk that is so strong. The stalks of plants have no wood in them, because they do not need it. They are strong enough to support the branches without having any wood in them.
Stalks of grain and grass have flint in them.
Some plants have their stalks made strong in a singular way. There is a flinty earth in them. This is the case with wheat, and rye, and most kinds of grass. See how tall the stalk of rye or wheat is. And it is very slender. But as the wind bends it over it does not break, because the flint in it makes it so strong.
It is this flint in different kinds of straws that fits them to be used in making hats and bonnets. They would not be firm enough for this use if there was no flint in them.
You can not see or feel the flint in the straw. The reason is, that the particles of the flint are so fine, and are so well mixed up with the fibres or threads of the straw. It is this fine flint in straw that makes its ashes so useful in polishing marble. In some plants you can feel the roughness that is made by the flint. You can feel it in the scouring-rush, which is sometimes used by house-keepersin scouring. In this there is more of the stony substance than there is in the straw of your hat, and it is not as fine.
How flint gets into stalks.
But you will ask how stone or flint gets into these plants. It is sucked up from the ground by the mouths in the roots, and it goes up in the sap to where it is wanted. It is wanted in the stalk of the grain, and so it stops there. It never makes a mistake by going into the kernels of the grain. If it did, the flour that is made from them would be gritty, as we should find out when we came to eat the bread.
Shrubs.
All plants that have no wood in their stalks die down to the ground in the autumn, though the roots of some of them live through the winter. But trees, you know, remain from year to year. So do shrubs and bushes. These may be considered as little trees. Some shrubs are so small that they do not need to have their stalks woody merely to support the branches. Thus the currant-bush could have its branches well supported if the stalks were not woody. In such cases the stalks are made woody so that they may last over the winter.
Vines.
Stalks and trunks commonly stand up of themselves. But there are some that can not. When this is so we call the plant a vine. Vines are supported in various ways. Some are held up by merely winding around something. This is true of the bean-vine. It winds itself, as it grows, around the pole that is put up for it. The hop-vine is supported in the same way. It is, you know, quite rough, and so it can cling firmly even to quite a smooth pole.
Tendrils.
Pea-vines are held up in a different way. Little tendrils areput forth which wind around the branches of the bushes that are set for the vines to run up on. These tendrils clasp very tightly. You see them on many kinds of vines. You see them on grape-vines, and on the vine of the passion-flower. Sometimes the tendrils go out from the ends of the leaves. You see a leaf of this kind on page 68.
Thunbergia.
A vine called thunbergia is held up in a very queer manner. If a leaf happens to come near a twig or a string it twists its stem around it. So the stems of the leaves act as tendrils to support the vine.
Trumpet-creeper.
The vine of the trumpet-creeper is supported in a singular way. Whenever it touches any thing there come out at the joints of the stalks some sprawling things like the feet of a spider. These feet fasten themselves very strongly to whatever the vine is running on. If it runs up the side of a board fence, these feet mix up their fibres very tightly with the fibres of the wood. It is curious to observe that where any part of the vine is not against any thing these feet do not appear. They are made only where they can be used. The plant acts just as if it knew where it could use them.
Questions.—What is the difference between stalks and trunks? Why does a tree need so strong a trunk? Why do the stalks of plants have no wood in them? What is said of the flinty earth that is in some of them? In what ways is the flint in straws of use? What is said of the scouring-rush? How does flint get into any plant? Why does it not go into the kernels of grain as well as into the stalks? What becomes of stalks that are not woody in the winter? What is said of the woody stalks of shrubs? What are vines? How is the bean-vine supported? Tell about tendrils. What is said of the thunbergia? Describe the way in which the trumpet-creeper is supported.
Questions.—What is the difference between stalks and trunks? Why does a tree need so strong a trunk? Why do the stalks of plants have no wood in them? What is said of the flinty earth that is in some of them? In what ways is the flint in straws of use? What is said of the scouring-rush? How does flint get into any plant? Why does it not go into the kernels of grain as well as into the stalks? What becomes of stalks that are not woody in the winter? What is said of the woody stalks of shrubs? What are vines? How is the bean-vine supported? Tell about tendrils. What is said of the thunbergia? Describe the way in which the trumpet-creeper is supported.