英文科學(xué)讀本 第三冊(cè)·Lesson 55 The Seed-Leaves

Lesson 55 The Seed-Leaves

Would you like to learn a little more about those wonderful seed-leaves, Norah? asked Fred. "There are a few things about them which we ought not to forget."

Oh yes, do tell me, Fred, said Norah. "The more I know about all these wonderful things, the more I want to know."

Well then, said Fred, "the seeds which I brought you to examine had all of them two seed-leaves, and the germ itself formed the little hinge to hold the two parts together."

Let us take the scarlet bean seed once more. Open it and you will see that it has double seed-leaves. But I want you now to look not at the seed, but at the green leaves of the plant. Here are some of them.

Hold one up to the light and tell me what you notice about it.

Oh, I know, said Norah. "You mean the veins. These are net-veined leaves. The veins branch out and spread through the leaf in all directions."

Quite right, Norah, said Fred, "and now I want you to examine some other seeds for yourself. Here are some large seeds such as apple-seeds and pear-seeds, plum and cherry stones, almonds, acorns, and peas. Here, too, I have some small ones—radish seeds and mustard seeds. If you open them you will find that every one of them has double seed-leaves."

Now take them one by one and think what kind of leaves they produce when they grow up into plants. The apple tree and the pear tree, the plum and cherry trees, the almond tree and the oak all have the same net-veined leaves. So have peas, radishes, and the mustard plant.

In fact, you may say that all plants bear net-veined leaves that come from seeds with double seed-leaves.

But what about the plants with parallel-veined leaves—leaves whose veins run side by side? asked Norah. "Haven't these got double seed-leaves too, Fred?"

No, said Fred, "they have only one seed-leaf. I can't tell you anything about those now. Teacher has promised to give us a lesson on them tomorrow."

SUMMARY

The bean seed has two seed-leaves. The plant which comes from it has net-veined leaves. All plants with net-veined leaves come from seeds which have double seed-leaves.