The Thee as an Invention

APRIL, 1929

BY CHARLES D. STEWART

I

A MAN without bones would lie flat as a flounder. He would be as unable as an oyster to raise his head or stand upright. The skeleton, that core of life he leaves behind him to be dug up by the ologist and displayed in all its completeness behind glass, is the thing by which he performed his comings and his goings, and without which he would have lived a life without works. It was bones that raised him up and made him the king of beasts, an animal standing on end with a tool in either hand. It was by means of them that he got up from the ground and took on the image of the cross, a man and not a worm.

But while the stiffening structure is thus important, it is far from being the vital part of him. This is lime and not life; mere mineral from the quarry. Those hinges did not work themselves, nor did those bones keep their own balance. It is but a trellis — those tubular legs and those latticelike ribs — by which the living creature lifted itself from earth and stood a few feet nearer heaven. Rather it is the prop that held up the tent of life; for while he could not have stood without it, neither could it have stood without him. Before coming to the public museum it was in actual operation, with errands here and there; and now the holiday visitor, who came to see the stuffed bear and the zebra, may stand and stare, with such mind as he may have, upon those stark levers which the spirit has used as a crutch. Somebody, somewhere, may be said to have died and disappeared. But this substantial part of him would be able to stand here for centuries, holding the mirror up to nature on Sunday afternoons.

A tree is in much the same case. Its solid body is all skeleton, and the skeleton is essentially dead. In any tree, however live and growing, the substance composing trunk and branch is inert and lifeless matter. The heartwood of a tree, the heaviest and solidest part, extending a considerable distance from the centre, is dead in every sense of the word. Its tubes no longer convey the sap upward, because their walls have become thickened and filled with lignin. In them there is not even the semblance of vital activity. From the heartwood outward to a point very near the surface we find the waterconveying structure consisting of long tubes; and these tubes are mere conduits, inert and lifeless. They serve a useful purpose in conveying the water upward, but they are not themselves alive. At first, when they were being built, there were live cells working inside of them, little bags of protoplasm; but, once they were completed, the live tenants disappeared. Interspersed among these tubes is tissue which still contains protoplasm, but it is not alive in the sense that it can grow or reproduce itself.

Copyright 1920, by The Atlantic Monthly Company. All rights reserved.

The only part of a tree that is really alive, in trunk and root and branch, is a thin sheath of cells at the surface of the wood called the cambium layer. It is this live part that keeps building and making the tree larger.

When a tree is cut down, the circling grain on the stump tells something of the age and the story of growth. But if we were to saw the whole tree into small sections or divide it lengthwise with a view to tracing the course of these rings all the way to the top, we should learn something more of a tree’s inner nature. A cut across a tree near the ground may show three hundred annual rings, while cuts at higher points will disclose but a hundred, or fifty, or forty. The rings become fewer and fewer.

If we take a particular ring and follow it up we find that it grows smaller and smaller till it diminishes to a point, a ring near the centre of the stump coming to an end at no great distance from the ground, while one a greater distance from the cent re reaches to a correspondingly greater height. And each of these rings, according as it is the fortieth or fiftieth or hundredth from the centre, will show the height as well as the thickness that the tree has attained in that number of years. As anyone can see by its mere outer form, a tree grows smaller upward, tapering from a considerable girth at its base to a fine point at its extremities. And when we examine these inner sheaths of annual growth we find that they do the same. All the successive surfaces of the tree are enclosed here, from the giant form of the season just past down to the little sapling of another century.

Thus we see what a tree really is. It is a sheath of life spread over the dead trees of other years. Generation stands within generation, successively wrapped about. The outer life of cambium and leaf and bud uses this as a trellis to go up and reach out sunward and skyward. Instead of throwing its old skeleton aside each year and starting anew, it clings to its dead bones, profits by their stature, and makes tubes in them to provide the supply of water for a larger and more ambitious growth. A tree is a building, a tower, a specialized skeleton, serving the purposes of life. When we compare this way of growth with other methods, both animal and vegetable, it must strike us as a most interesting invention.

As the inner or lifeless part of a tree is incapable of growth or upward expansion, a nail driven into a young tree at any particular height will remain at that distance from the ground throughout the life of the tree. And a branch coming out at any point will not be carried upward as time goes on.

In the giant Sequoia of California we have trees whose long life is a matter of constant marvel. But the part of them that is really alive is of quite recent growth. A sequoia may be three or four thousand years old, and an oak or elm three or four hundred, provided the inner part, which was actually in existence that long ago, is not rotted away and represented by mere space. Of course the cells in the superficial living parts of such trees are descended from cells of thousands of years ago; but so are the cells in the body of the human beholder.

II

In the essential matter of life and death, a tree presents two great points of difference from an animal. An animal is alive all the way through, even its bones, tendons, and cartilaginous parts containing live cells which are engaged in the work of upkeep and repair. As we have seen, a tree is not alive all the way through, the bulk of its body being all skeleton and dead. But when we consider the live tissue that its skeleton supports, we find that the tree offers a different sort of contrast. An animal grows rapidly at first. It has an exultant youth. The human being, in the original cell which contains the whole beginning, measures but .004 of a cubic centimetre. By the time the child is born, it has increased — by one of those biological feats of geometrical progression — to a billion times that size. Here nature steps in with inhibiting hand, and the life processes begin to slow up, so that, from his babyhood to his twentieth year, a man has increased but sixteen times. At this point all growth stops, and the vitality steadily declines until finally the forces of life and death are just about balancing one another and the machine may stop in an instant.

Take note of a tree and consider how different all this can be. A tree never loses the vital power of growing. It starts out as rapidly, retains the power of geometrical progression, and is ever young. There seems to be no reason in itself why a tree should not live forever. The aged man, looking up at it, finds it a synonym for his hopes and speaks of ‘the tree of life.’ If he has achieved threescore years and ten, he thinks of the tree and refers to his own efforts at living as a ‘green old age.’

And so, if the tree is, in some respects, as dead a thing as any we see in nature, it is, in another regard, the livest example of all life. The power to grow is the very ultimate manifestation of vital power. It is a continual triumph over death. When we look upon a tree we should think not how old it is, but how young. It is as youthful in fact as the most inexperienced shrub or sapling around it.

A hard bone, while it has living cells scattered throughout its substance, consists nevertheless of a large proportion of inert or nonliving material; and as this mineral substance is not expansible or st retchable, the bone has a problem of growth to solve. It can be solved in but one way. The bone grows entirely by the propagation of new cells on its surface. They build layer on layer, thus adding to its girth. The bone grows thicker in the same way that a tree adds to its wood, and for the same mechanical reasons. In the matter of growing longer, or taller, both tree and bone face the same problem of hard inner material that is inert and inexpansible. The tree accomplishes its increase of stature and wider reach by means of buds and soft, expansible tissue at its extremities. When these tender extensions grow older they harden into wood, and then the terminal buds spring forth again to add to the annual growth. In view of the obvious necessity of this way of growth, one might logically expect that a long bone, as in the arm or leg, would add to its length simply by growth at the end, the surface cells building in the usual manner. But here a difficulty intervenes. The joint, constant ly working and needing to be faced with a specially lubricated cartilage, makes the scheme impractical. And so there is preserved, near each end of the shaft of the bone, a semisoft or unossified region; and while the rest of the bone is taking in lime and hardening, all longitudinal growth takes place in this limited and softer section. The bone first hardens in the midway region, where stiffness is needed, and at the ends under the lubricated bearings; and care is taken that the growing part is not intruded upon till the animal is reaching maturity. When the animal has been brought to full size, lime is deposited here and hardening takes place. In the human being this growing state of bone may last till the twentieth year. From this we see that in wood and bone, when conditions are the same, a like mechanical principle is employed, and when conditions are different the method is altered to meet them. Always new problems make call for new inventions.

While a tree agrees with bone in the way of adding girth, and differs from it in procedure at the end of the branches, the roots face a different set of circumstances. A root has to push its way continually through rock and sand and hard impacted earth, and yet it must achieve this growth by means of soft and tender tissues that make such rough contact impossible. In this case there is developed, on the end of the growing tissue, a tough, hard growing-cap consisting of cells that have differentiated for the purpose, and these serve to protect the cells behind and plough the way for them. The growth therefore takes place in a region a short distance from the end; and this is similar to the technique practised by bone. So, while wood and bone may differ in points of practice, they seem to end in a harmony of opinion. The moral of which is simply that logic is logic and a good mechanic is a good mechanic.

III

A tree, like other forms of life, is engaged in the constant circulation of fluid through its tissues. Life processes, animal or vegetable, can go on only so long as each individual cell is surrounded by a fluid containing nutriment. To meet this demand and to provide for a large amount of evaporation, a tree passes up a great deal of water. A fairly large beech tree will use about sixty-five gallons of wat er on a dry, hot day, while a large oak will require much more. Even a sunflower will use two pounds. And this water, in the larger species of trees, will have to be lifted two hundred and even three hundred feet.

Anyone who is familiar with pressures in a tall standpipe or water tower, or who has even taken up the problem of raising water to the second story of a country residence, must be interested in asking, How is this supply of water taken to the top of such tall trees? This question, in the present stage of man’s knowledge of physics, cannot be answered. We do not know.

I dare say that anyone with an everyday knowledge of physics, such as might be learned from a lamp wick, would be able to suggest ways and means of getting the water up there; but it would be difficult to think of anything that has not already been considered and found wanting. The lamp-wick principle, capillary attraction, will not go far in raising water. Water rises in a capillary or fine tube to a height in proportion to t he fineness of the tube; and the viscosity of water is such that if the tube is very fine it will not rise at all. Capillary attraction would not raise water to the top of even a moderate-sized tree.

Root pressure or osmosis, a sort of powerful absorption due to unbalanced chemical pressure between the soil water outside of the root membranes and the denser solute inside of it, has been taken into consideration. By cutting off a plant near the ground and fastening a glass tube upright on the stem, it is possible to ascertain the height to which its sap will rise by pressure from below. Under favorable conditions a grapevine will exert a pressure sufficient to raise a column 36.5 feet, while a birch has tested as high as 84.7 feet. This might seem a promising line of inquiry were it not that root pressure takes place in woody plants only in early spring, and especially in the morning. It has been found that when the tree is evaporating the greatest quantities of water, on dry, hot days of summer, there is no root pressure whatever. This fact, once it. was established, naturally set root pressure aside and left the problem unsolved. Even if such pressures were not seasonable and unusual, they would not serve to send water to the tops of the tallest trees.

It has been proved beyond question that the rise of water in the tubes of a tree is caused by a pull from above. That there is a strong pull upward can be demonstrated by means of any branch taken from a growing plant. Such a branch, if its cut end is inserted in an air-tight manner in a glass tube, will draw a supply of water from the tube with such force as to pull a column of mercury up after it. This demonstration, one might suppose, would set us definitely ahead in the solution of the problem. But here a difficulty intervenes.

The nature of the difficulty will be quickly apprehended by anyone who has had to learn the laws of an ordinary cistern or suction pump. A suction pump at its best will lift water but thirty-three feet; consequently it is not advisable to install one in the third story of your house. Since a column of water is not strongly cohesive, and since you cannot take hold of the end of a long pipeful of water and pull up any quantity desired, as if it were a rope (a ridiculous enough supposition, let us say), it can be lifted from above only by suction. The pump, by the lift of its piston, removes air pressure from the upper surface and tends to create a vacuum, in consequence of which the water is pushed up the pipe from below by the weight of the atmosphere, a pressure of fifteen pounds to the square inch at sea level. The weight of water being what it is, such pressure will balance a column of thirty-three feet. No invention can be made which will pull more than the laws of physics will enable it to. And thirty-three feet falls far short of reaching the top of a sequoia.

But water has got to go up those tubes to the top of a tree. It will and does. This being the case, scientists began to consider whether water in thin columns, as in these fine tubes, has not an actual power of coherence, a tensile strength, sufficient to stand a strong pull. Possibly, after all, water may be drawn up from the top as if it were a rope. Strange as it may seem, experimentation has gone quite far in proving this to be the case. It seems that such a column of water has a power of coherence great enough to withstand the pull. And the osmotic force in the leaves, a strong pull of absorption, might be sufficient to raise the columns of water to the necessary height. This is the theory that at present comes nearest to satisfying scientific minds. But further experimentation has caused more difficulty to appear.

The rise of water to the top of a tree is dependent upon evaporation. It is evaporation that makes room for the continual upflow of water; and it is evaporation that causes the chemical concentration in the living cells which gives rise to the strong absorptive pull, or osmosis. This being true, one thing is evident. If a plant, or a branch of a tree, is placed in an atmosphere so saturated with moisture that evaporation is impossible, it will be unable to keep the water flowing up its stem. Experiment has shown that the intake persists, though it is slowed up, even when the leaves are entirely submerged in water. It is difficult to see how this can be unless the leaves have some way of secreting or disposing of the water regardless of evaporation.

IV

Everything considered, we may say that the rise of the water is a mystery, provided we do not mean to imply that there is anything mystic about it. Of course we all know that it is life that is at work here — but life in which sense? On this point we have got to take our stand with the vitalists, whose doctrine is that ‘the functions of a living organism are due to a vital principle or force distinct from physical forces,’ or else we must enlist on the side of the mechanists as one ‘who regards the phenomena of nature as the effect of forces merely mechanical.’ In either case we find ourselves projected into the middle of a field of battle, and it behooves us to lay about. As for myself, I am bold to say that I listen most respectfully to the mechanist at all times when I am trying to add to my scientific knowledge, and I am considerable of a vitalist in those moments when I am essentially a poet, a prophet, or a seer.

It is really a religious war, the issue being between the believer and the biologist. And it is easy to understand why the scientist becomes nettled when he is informed by a vitalist that the thing he is trying to take apart is ‘life.’ The intention of this is to discountenance such activity, and thus to limit investigation. This is to set bounds to the pursuit of knowledge — a thing we must all fight against. Truth must have a charter free as air. The scientist, also, must hitch his wagon to a star. But, in spite of this noble aim, his opponent calls him a materialist, forgetting that this is no reproach at all; for who ever hoped to put the immaterial in a test tube or get a chemical reaction out of nothing? And so the scientist rebukes the vitalist by calling him an obscurantist — a name with quite a sting to it.

The whole matter might be open to clarification and amicable settlement were It not that the scientist, the biochemist, has fallen into the habit of staying away from church. His pew is quite empty. Having found his vocation misunderstood and wholly discountenanced, he has fallen away from the company of the elect and has about decided to take vows in one of the irreligious orders. Possibly this modern matter is correctly analyzed in the very up-to-date rhyme: -

It is when we consider the tree from the standpoint of evolution — a plant made to conquer difficulty, a sea creature living on land, a machine progressively put together to achieve the nearly impossible — that we begin to see its lofty waterworks in their full significance. The tree was an idea in nature, a very bold and original idea based upon a fundamental patent; and the steps leading up to it were four. First in the order of development came the primitive water plants, the thallophytes, floating freely about or, according to the latest views, living in the saturated soil along the shore. And in those days there were no other kinds of vegetation. Second came the amphibious plants, such as the mosses; third the woody plants beginning with ferns; and fourth the most modern woody and two-sexed plants of this highly mechanized vegetable age.

While we are getting our mental bearings we shall find it interesting to pause a moment among those lowly amphibians, the mosses. Here we see vegetation crawling on its belly up toward the dry land. Stealthily and cautiously it draws away from the water’s edge, lying low. It must not venture far, for it has no true roots; and it cannot and dare not raise its head out of the moisture. Behind it, in the order of creation, are the onecelled water plants, floating and moving about. They have no evident organs but the single cell; and they take their food, as cells have always done, by absorbing it from the liquid in which they are immersed. The moss itself consists of such cells, now banded together. At first it was but a thin sheath of them, lying flat on the mud; then it became several cells thick, the moisture being passed from the cells below to those above by absorption.

Finally — and it would not be at all inconsistent with evolution if I had said ‘suddenly’ — the great idea came to pass in the form of the fern. Here was a vegetable mechanism with true, running roots, which the moss has not; and it possessed a woody stem provided with tubes for conducting water. With the invention of the fern, piping the water upward, while the roots struck down to bring it from below, nothing more was necessary to the making of a tree. It only remained for the stock company of cells to go ahead and, in modern parlance, construct a ‘bigger and better’ plant.

Between the moss and the fern we might expect to find many imperceptible stages of evolvement. But evidently there can be no such thing in these cases. A thing either is or is not. You either have a tube in principle or you have not a tube. An idea always comes suddenly into existence, however long the preparation may have been. Therefore it has seemed to me that the idea of doing away with missing links in the scheme of evolution is positively silly. Between every fact and the one beyond it is a missing link; and it can only be filled in by answering a question: Was this thing a product of mind or did it just happen? One may answer as he pleases, but he can hardly get away from the question by any talk of evolution — nor by the search for any finer degrees of gradualness.

Imagine some primeval promoter addressing a company of those waterinhabiting cells and proposing the whole idea. Come now; our idea is to take a lot of you cells and build a tall plant living on land. Some of you are to be hung high up in the glare of the sun; you will stay aloft, and absorb the hot energy of summer while you make food for cells that are differently engaged. You must become specialists; and you are to give up this one-cell, jack-of-al1-trades idea. We are going to build a tree.’

A shiver of fear and consternation would certainly seize upon any waterliving cells that had the power to think. ‘Impossible!’ they would exclaim. ‘We should all die. Water is our food and life. We must be immersed in the water. A thing like that would never do.’

But that is just what came to pass. And every cell in the top of a tree continues to be immersed in the lifegiving water. Between a cell in the sea and one in the topmost twig there is no essential difference of situation. And the reason is that everything is done to control evaporation and hold it within bounds. Every leaf is coated with a preparation that most effectually seals it. Air can enter and water escape only through microscopic openings called stomates on the under sides of the leaves; and every stomate is capable of being opened or closed according to conditions. The whole trunk and every limb of the tree are jacketed in the protective, suberized bark. There is nothing more waterproof than bark, more stubbornly impermeable. It is because cork is so waterproof that it makes stoppers for bottles and gaskets for engines. It is because it is so impermeable that it is ground up to make linoleum. A tree, from head to foot, is armored against evaporation. Consequently its cells, though they hang in the very eye of the sun, are in water as wet as that which surrounded them in the sea.

V

It is when I look at a tree from this point of view that I feel like pinning — or nailing — a medal on its chest. If a man is the height of achievement in the animal world, so is a tree in the vegetable. A bronze tablet really ought to be hung on a tree here and there to memorialize scientific facts. I can imagine no one wearing the decoration more pompously than certain big, fat, burgherlike beeches of my acquaintance, or more worthily than certain rugged oaks or graceful elms. The inscription could be a very simple one, as, for instance: —

HERE STANDS
THE KING OF VEGETABLES
A SEA CELL THAT BECAME AMBITIOUS

A tree manufactures its food direct from earth and air, a thing the animal cannot do; and though it has no lungs, nor anything corresponding to such a mechanical device, it feeds life’s constant fires by taking in oxygen night and day. And how can a tree breathe without lungs?

The answer to this question might well be, In about the same manner that insects do. A bee, for instance, has no lungs. It has seven pairs of openings, called spiracles, along the sides of its body, these being the mouths of air-conducting tubes which, as they lead inward, branch off and become finer and finer so that they ramify the whole living structure as do the capillaries which distribute the blood in an animal. That is to say, the oxygen, instead of being delivered indirectly, by chemical combination in a stream of blood, is taken direct to each cell in the body in the form of air. In a tree, the air enters through openings called stomates on the bottom sides of leaves; but there are no air tubes continuing these openings for the reason that the leaf is but a thin sheath of life, only a few cells thick, and there are open spaces all through the inner structure in which air may circulate freely. Along the sides of a tree, too, in the bark, are porous openings, and these serve to let in air as do the spiracles in the fly, the grasshopper, or the bee. The little short marks on the bark of birch, and on the smooth exterior of plum and cherry, are such porous breathing places. While these lenticels are not so evident on the rougher trees, they are none the less there. An insect speeds up the intake of air by a panting movement or telescopic working of its segments, whereas a tree, being such a thin sheath of life, can depend upon the natural interchange of gases by chemical or physical laws. But a tree and an insect work alike in the regard that they both receive their air directly and at first hand.

I think that our understanding of the life processes of other beings is much handicapped by the natural supposition that our way is the only way. If the surfaces of the lungs were spread out freely to the atmosphere, like the leaves of a tree, the breathing mechanism would be unnecessary. The red corpuscles, coursing through the fine tissues of the lungs, give off their carbon dioxide and take in oxygen from the air by their own sole power, and not by any virtue of the mere act of breathing. It is only because we lake our air through a small tube, and because our aerating machinery is so compact, that this bellowslike movement is necessary.

Our likeness to a tree would be much less obscure, also, if we remembered that it is not a man who needs air and takes in food, but the cells of which he is composed. For instance, a man takes a deep breath. The red corpuscles absorb from it their load of oxygen; but as Yet the breath has been of no benefit . The red corpuscles hurry it on to its destination, coursing through capillaries microscopically small. But so long as it is in the capillaries the oxygen has not yet arrived. It must pass through the thin walls of these small blood vessels and get into the lymph which bathes each individual cell in the body. And the living cell, immersed in that lymph as in the primeval sea, takes up its supply by osmosis or by some live power of selection and absorption the whole nature of which is a mystery. It is thus that the breath arrives; and thus, also, the food comes and is absorbed from the same stream.

From the standpoint of evolution, or even of present-day matter-of-fact, a cell deep in the leg or arm of a man, or hung high on the leaf of a tree, is in essentially the same circumstance as a primitive one-celled animal floating or crawling about and absorbing its food and air direct from the water. All cells, animal or vegetable, are essentially alike in structure; they live on the same sort of food and take it in the same way. It must be in liquid form; not in mere suspension or emulsion, but in true solution. As the cells in a man are confined to one place, and cannot float or wander in a stream or a pond, the nourishing stream is made to flow past them. It all amounts to the same thing. Because our cells are so deep-seated, so specialized, and so far from the free food and oxygen of nature, we have need of all this intricate machinery and this digesting and food-preparing laboratory. But all the time it is the cells that are doing the living, and supporting and coöperating with one another in this strange stock company. It is in this sense that Thomas Edison is speaking when he says that ‘man is a colony.’ Being, of all men, mechanical-minded, one might expect him to regard the human animal as a machine. But he is thinking of the builders and operatives — the cells themselves.