The Adventures of a Grain of Dust Part 21

The roots, like all parts of the plant--like all parts of boys and girls and grown people, for the matter of that--are made up of little cells.

Well, these cells, first on one side of the root and then the other, enlarge, and so pump in an extra flow of sap. Now, as we know, the sap contains food for the plant, just as blood contains food for our bodies; and more food means more growth. So the side of the root where the cells first swell out grows fastest and thus pushes the root over on the opposite side. Then the cells on this opposite side swell, and the root is turned in the other direction again. So it goes--right and left, up and down. And when these two motions--the up and down and right and left--are put together, don't you see what you get? The round-and-round motion!

Precisely the same thing happened right now when you turned your finger round and round to imitate the motion of the root. (I saw you!) The muscles that did the work swelled up first on one side and then on the other, just as they do when you bend your elbow, when you walk, when you breathe, when you laugh.

And more than that: You know how tired you get if you keep using one set of muscles all the time--in sawing fire-wood, for example. Yet you can play ball by the hour and never think of being tired until it's all over; because, for one thing, you are constantly bringing new muscles into action as you go to bat, as you strike, as you run bases. It's the same way with the roots, it seems. For the theory is that after the cells on one side have swelled, they rest; then the cells on the other side get to work.

"But what starts the movement?" you may say. "The idea of moving my arms and legs starts in my brain."

WHERE MR. ROOT KEEPS HIS BRAINS

Just so again. The root has a brain, too, or what answers for a brain.

And the root's brain, is in its head; at least in the vicinity of its nose--that is to say, its tip. It's the tip that first finds out which side of the road is best, and pa.s.ses the word back to the part of the root just behind it to bend this way or that. It's also the tip that feels the pull of gravity and knows that it's the business of roots to keep under cover. And Mr. Root just _will_ have it that way! You can't change his mind. Mr. Darwin tried it and he couldn't; although he finally changed human people's minds a lot.

[Ill.u.s.tration: WHERE MR. ROOT WEARS HIS CAP

A root wears its cap right where you do--over its brain department; that is to say, the tip. It is called the "root cap" and protects the tip from injury.]

This is how he tried it on a root. He took a bean with a little root that had just started out into the world. He cut off the tip and then set the bean so that the root stuck straight up. It continued to grow that way for some little time. Finally, however, a new tip had formed.

Then there was a general waking up, as if the tip said to the rest of the root:

"Here, here, this will never do! Where are you going? You must bend _down_!"

Anyhow that's what the root proceeded to do. One side seemed to stop growing, almost, while the other side grew rapidly and so the bending was done.

"Did you ever! But how does the tip send back word?"

"Don't ask me!" says the science man; say all the science men, even to this day. "We don't know yet just _how_ it's done. But we're studying these things all the time, and we'll know more about it by and by.

Meanwhile, perhaps you'll tell _us_ why you say 'ouch' and pull your finger away when you touch something hot."

"Oh," you reply, "I say 'ouch' because it hurts; and teacher and the Physiology say my arm pulls my hand away because my head tells it to."

"Yes, but how does the head make the arm do the pulling? What's the connection?" says the science man.

Well, I guess we'll have to tell him we don't know, won't we?

But all the root's brains aren't in the tip, any more than all _our_ brains are in our heads. Scattered through our bodies, you know, are _little_ brains, the ganglia, that control different parts of the body.

So it is with roots. For instance, a root at a short distance from the tip, is sensitive to the touch of hard objects in such a way that it bends toward them instead of turning away, as the tip does. The result is that when a root comes to a pebble, say, under ground, the sides of the root press close up to the sides of the pebble--turn around corners sharply, by the shortest route--and so get over the obstruction as soon as possible and resume their course in the soil.

[Ill.u.s.tration: BUT THEY COULDN'T CHANGE ITS MIND

Some sprouting seedlings were attached to a disk like that, and when the roots started to grow down, the disk was turned to make them point upwards. But, no Sir! The roots just _wouldn't_ grow upward. They turned downward. Every time!]

And different parts of a plant's root system respond in different ways to the pull of gravity, and some don't respond at all. The tap-root, for example, which always grows down, has roots growing out from it horizontally. They just won't grow any other way, and yet this is also supposed to be due to the influence of gravity. Then, from these horizontal roots, grow out a third set, and they don't seem to pay any attention whatever to gravity. They grow out in all directions--every which way--so that if there is a bit to eat anywhere in the neighborhood they are reasonably sure to find it. You see it works out all right.

When a plant first begins to peep into the world out of that wonder box we call the seed, it's the root, as we know, that does the peeping; it comes first. And its first business is to get a firm hold in the soil.

So a lot of fine hairlike fibres grow right and left and all around and take a firm grip. There is an acid in the root that dissolves whatever the root touches that has any food in it--including pebbles and old bones--and so makes a kind of sticky stuff that hardens. In this way these fibrous roots not only get good meals for themselves and the rest of the plant, but they hold the plant firmly in the soil, against the strain of the winds. They also give the tap-root something to brace its back against, as it were, while it pushes down for water, for the moisture in the damper portion of the soil beneath.

As you may have noticed, a seed merely lying loose on the ground is lifted up by its first little root in its effort to poke its nose into the soil. But Nature makes provisions for covering seeds up. They are covered by the castings of the earthworms, the dirt thrown out by burrowing animals and scratching birds. Some seeds fall into cracks where the ground is very dry and others are washed into them by the rains; while these as well as seeds lying on the surface are covered by the was.h.i.+ngs of the rain. Then come the roots that grip the soil.

Always growing just back of the tip, are thousands of root-hairs, as fine as down. These get food from the soil. They soon disappear from the older parts of the root, so that it stops gathering food itself and puts in all its time pa.s.sing along to the stem and leaves the food gathered by the finer and younger roots. This is why plants are so apt to wilt if you aren't careful when transplanting them; the root-hairs get broken off. For the same reason, corn, after it grows tall, is not ploughed deeply. The fine roots reach out between the rows and the ploughshare would cut them off.

II. MR. ROOT'S PRESENCE OF MIND

All these things and more the roots do in their daily work--in the ordinary course of business. And it's wonderful enough. Don't you think so? But there are even stranger things to tell; things that would almost make us believe roots have what in human beings we call "presence of mind." That is to say, the faculty of thinking just what to do when something happens that one isn't looking for; when the house takes fire, for example, or the baby upsets the ink.

[Ill.u.s.tration: THREE SCHOOLS OF STRATEGY]

A ROOT'S WAY OF CROSSING A ROAD

Take the case of tree roots crossing a country road for a drink of water. They do it just as you or I would, I'll be bound. Just suppose you and I were roots of a big tree that wanted to reach the moist bank of a stream, and there was a hard road-bed between. We can't go over the top, and the road-bed is so hard we can't go straight through on our natural level so we'll just stoop down and go under, won't we? That's exactly what the roots do. They dip down until they get under the hard-packed soil, and then up they come again on the other side and into the moist bank they started for.

The roots of each kind of plant or tree have their natural level; that's one reason, as we know, why so many different kinds of plants--gra.s.s, trees, bushes, and things--get on so well together in the fields and woods. The tree roots that we have just seen crossing the road only went down below their natural level because they had to, as if the tip said:

"This soil is too hard. We can never get through. Bend down! Bend down!"

So the roots bent down until they came to softer soil, then forward, but always working up toward their natural level, and so it was at their natural level they came out on the other side.

A ROOT'S STRANGE ADVENTURE WITH A SHOE

But here's an example of "presence of mind," that n.o.body has accounted for. A good-sized root, working along through the soil, like Little Brother Mole, to earn its board and keep, came right up against the sole of somebody's old shoe that had got buried in the soil. In the sole were a lot of holes where the st.i.tches used to be. The root divided into many parts, and many of these smaller roots found their way through the st.i.tch holes. Then, coming out on the other side, these little roots got together and travelled on, side by side!

[Ill.u.s.tration: HOW THE RAG BABIES TELL THE FORTUNE OF THE SEED CORN

In what is popularly called "the Rag Baby Test" the seed corn is placed on squares marked on cloth with numbers corresponding to the numbered ears. Then they are rolled up in one of those moistened rags until they sprout.]

Isn't that a story for you? But there's no accounting for it. As we have seen, the men of science know a little bit about how a root manages to turn round and round and away from the light and so on, but what kind of machinery or process is it that could tell the root if it would split up into little threads it could get through the st.i.tch holes in that old boot? You can't imagine; at least, n.o.body so far has thought how it was done. But it's all true. We'll find the story and a lot of other things about the ways of roots in one of the books we'll get acquainted with when we come to the "Hide and Seek."

[Ill.u.s.tration: _International Harvester Company_

THIS IS THE ANSWER

The seed from Ear No. 12 came out beautifully, didn't it? That from Ear No. 13 looks as if they were superst.i.tious in Corn Land; but of course it was the fault of the seed and not of the number.]

Here's another example of the same thing; what we have called "presence of mind," resourcefulness, invention. This example is even more striking, if possible, because, for one thing, it is a case where roots still more completely altered their habits to save a tree struggling for its life on a stony mountain cliff. Maeterlinck tells about it in his picturesque and dramatic style. The subject--the hero, as it were--of this story was a laurel-tree growing on some cliff above a chasm at the bottom of which ran a mountain torrent.

"It was easy to see in its twisted and, so to say, writhing trunk, the whole drama of its hard and tenacious life. The young stem had started from a vertical plane, so that its top, instead of rising toward the sky, bent down over the gulf. It was obliged, therefore, notwithstanding the weight of its branches, stubbornly to bend its disconcerted trunk into the form of an elbow close to the rock, and thus, like a swimmer who throws back his head, by means of an incessant will, to hold the heavy leaves straight up into the sky."

This bent arm, in course of time, struggling with wind and storm, grew so that it swelled out in knots and cords, like muscles upholding a terrific burden. But the strain finally proved too much. The tree began to crack at the elbow and decay set in.

"The leafy dome grew heavier, while a hidden canker gnawed deeper into the tragic arm that supported it in s.p.a.ce. Then, obeying I know not what order of instinct, two stout roots, issuing from the trunk at some considerable distance above the elbow, grew out and moored it to the granite wall."

As if the roots, naturally so afraid of light, had heard a frantic call for help and, regardless of everything, had come to the rescue.

To be sure, certain roots--the prop-roots of corn-stalks, for instance, as you have noticed--habitually reach from above ground down into the soil, and serve to brace the tall stem swaying in the winds, but trees usually have no such roots and no such habits. Yet, here a tree seems suddenly to have learned, somehow, that elsewhere in the land of plants this thing is done. But how did it learn it? Did the brownies or the gnomes tell it; or was it some of the spirits of the wind that go everywhere and see everything? It might have been the same wind sprites that carry the seeds of the laurel and the pine so far up the mountain flanks. Or it might have been the dryads, those beautiful creatures of the wood the Greeks knew so much about.