Do You Know a Plant…

4

How a plant can grow on a bare wall?

One of the most important parts of the food of green plants is carbon, and the plant finds it, or rather carbonic acid which contains carbon, in the air. But that is not all. The plant must have water and must have salts.

When we begin to look at a bare wall closely, we find that it is not so bare as it seems.

First we may say that rain falls on it, and so the plant of the wall gets its water. Then rain contains small quantities of salts. As the rain goes down the wall, it gets more salts.

So we can see that plants can get even on a bare wall those things which are necessary for their life. But, of course, a plant which grows on a bare wall cannot get much food. So a plant on a bare wall can never reach a large size.

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Why a tree stops growing? We may ask the same question about men, or horses, or birds.

The growth of living things is not like the growth of a snowball. A snowball grows as soon as it gets more and more snow. There is nothing inside it that limits its growth.

But every living thing has something inside that limits its growth. We may say that every living thing grows to the size which suits it. After that it stops growing and lives as long as it can.

... that a growing plant can push very hard against anything that gets in its way? If soft, little ferns begin to grow underneath a sidewalk, they can crack the cement.