英文科學(xué)讀本 第一冊(cè)·Lesson 34 Leaves

Lesson 34 Leaves

You would have liked our lesson today about leaves, Norah. said Will.

Wouldn't she, Fred?

Yes, said Fred, "and I think we'll go out into the garden, and pick a few leaves for ourselves, and have the lesson all over again."

They were soon seated, with the leaves before them, and Fred began:—

Suppose we start with this one. It is a leaf of the lime tree at the bottom of the garden. Look, Norah, there are two parts to the leaf. This thin flat broad part is the blade. The long stalk which connects it to the branch is the footstalk. Look at all the leaves you have in your lap. Tell us which is the blade, and which is the footstalk of each.

Now look again, said Willie. "One side of the leaf is smoother than the other. The smooth side always points upwards to the sky. The underside is the rough one."

Let me point out something else, said Fred. "Look at the under side of the leaf. You will see some thick stout lines crossing the blade. They start from the stalk, and run to the edge of the blade. We call these the ribs. They are to support the blade, and keep it stretched out to the light and air."

But, said Norah, "I can see a great many other lines all over the blade. They are not so thick and strong, but they run allover it, and cross each other like a network. Are these ribs too, Fred?"

No, said Fred, "we call them the veins of the leaves. Nearly all the leaves you have in your lap have veins, which cross each other and form a network. Teacher tells us to call them net-vein leaves."

Now look at this lily leaf. Hold it up to the light. Do you see veins crossing each other in this leaf?

I can see the veins, said Norah, "but they run side by side, from one end of the leaf to the other."

Teacher says, added Fred, "that leaves of this kind have parallel veins, and this means that the veins run side by side, as you told me, Norah."

SUMMARY

A leaf consists of a blade and a footstalk. In most leaves ribs stretch across the blade, and veins spread over it in every direction. We call these net-veined leaves. In some leaves the veins run side by side. These are called parallel veined leaves.