英文科學(xué)讀本 第一冊·Lesson 37 More about Leaves

Lesson 37 More about Leaves

We have learned some new things about leaves today, Norah, said Fred, "and I want to try and tell you all about it. But before I begin you might think of some of the things we told you about leaves the other evening."

Well, said Norah, "I know that all leaves have veins running through them. In some leaves the veins run side by side, but in most of the leaves the veins spread about in a sort of network. The veins all come from the ribs, which stretch across the blade, and the ribs spring from the footstalk of the leaf."

That's very good, said Fred. "Now listen, while I tell you the most wonderful thing of all about the leaves."

Teacher says that the surface of the leaf blade is crowded with tiny holes or pores.

I suppose, said Norah, "our eyes are not sharp enough to find them, for I cannot see them."

No, said Fred, "we children can't see them, but they are there, Norah. They are breathing pores. The leaves breathe in air through these pores."

You know what the root-hairs do?

Oh yes, said Norah, "They absorb liquid food from the soil."

Well then, said Fred, "this liquid food rises upward through the stem and branches, and along the footstalk till it reaches the leaves. Teacher says the earth-food, which the roots absorb, is no use to the plant till it has passed through the leaves. It flows through the footstalk, then through the ribs, and then the veins carry it all through the leaf. While it flows through the leaf, it absorbs some of the air, which the breathing pores take in. It is this that makes the liquid into food fit for the plant."

SUMMARY

The surface of the leaf-blade is crowded with breathing-pores. The leaves breathe in some of the air through these pores. This makes the sap into food fit for feeding the plant.