英文科學(xué)讀本 第一冊(cè)·Lesson 31 The Stems of Plants

Lesson 31 The Stems of Plants

Suppose we have a chat about the stems of plants, said Fred. "The stem, you know, makes its way upward from the ground, to get as much light an air as it can for the plant.

The stems of plants are not all alike. Let us take the trees first.

They live year after year. They have a hard woody stem, which we call the trunk. At the top of the trunk are the branches. Bushes and shrubs have a great have a great many stems, but they too are hard and woody.

But, said Norah, "most of our plant in the garden either die down to the ground or perish entirely in the winter. What do we call them, Fred?"

They are called herbs, said Fred. "They have soft green stems."

These herbs too, said Willie, "have all sorts of stems. Let us try and think of what teacher said about them."

Well, said Fred, "most of them, as we can see by looking round the garden, have strong, stout, upright stems.

Some, like the scarlet-bean and the hop, are not strong enough to stand upright. We put tall sticks beside them, and they twine themselves round the sticks. We call them twining stems.

We train the sweet-peas on the trellis for support, said Willie, "but they are not twining plants. They have little curling tendrils here and there, which cling round the trellis. The vine and honeysuckle have tendrils too. We call these climbing plants."

Now come and look at these strawberry plants, said Fred. "See, as the plant grows, it sends out slender stems along the ground. These we call runners. Each runner sends down, at the next joint, a great many new roots. Plants of this kind we call creeping plants."

I have one more stem to show you, he went on. "We will pull up this root of mint. See, here are the roots. But what are these thick white cords, which run out from the root?"

If you look, you will see buds here and there along the cords. This proves that these cords are not roots, but stems. We never find buds on roots. We call stems of this kind underground stems."

SUMMARY

The stem of the plant makes its way up towards the light and air. Stems are not all alike. Trees and shrubs have hard, woody stems; herbs have soft green stems. Some stems are very slender and weak. There are twining stems, climbing stems, creeping stems, and underground stems.