英文科學(xué)讀本 第一冊(cè)·Lesson 29 The Root and its Work

Lesson 29 The Root and its Work

Now, Norah, said Fred, "shall we have another chat about the roots of plants? We did not finish all I wanted to tell you last time."

Oh yes, do. said his sister.

Then tell me, said he, "what the root has to do for the plant."

It has to hold the plant firmly in the soil, said Norah, "so that the winds and the rain may not tear it up. It has, besides that, to feed the plant with food from the soil."

Quite right, said Fred. "Now I am going to try and tell you how the root feeds the plant. Come out into the garden, and we will get some roots. Suppose I dig up this carrot."

Now look, he went on, "at these fine, white threads all over the carrot. Teacher says they are the root-hairs."

Yes, said Willie, "and they have more to do than any other part of the root. They are the feeders of the plant."

Will is quite right, said Fred. "Every morsel of food, which the plant gets from the soil, has to pass up through those little hairs."

Teacher told us, he went on, "that these root-hairs are made up of a great many tiny cells or cases, with the thinnest of thin walls. Our eyes are not sharp enough to see them now. But that is what they really are. The thin cells act very much like a sponge. The sponge, you know, absorbs liquids. These root-hairs do the same."

Now just think over our chat about rock-salt. What happens when the rain sinks into the ground and washes through the salt-beds down below?

Oh, I know, said Norah. "The water dissolves the salt and carries it away."

Quite true, said Fred. "Now in the soil of our garden there is all that the plants want for food. But it is no use to the plant, till the rain sinks in, and dissolves it. If the plants do not get water they droop and die. They die because they are being starved. There is plenty of food for them in the soil, but the root-hairs cannot absorb it, till the water comes to dissolve it."

SUMMARY

The root feeds the plant with food from the soil. The root-hairs are the real feeders. They are made up of a great many very small cells, with soft, thin walls. These cells take in food, which the rain dissolves out of the soil, and pass it upward to feed the plant.