Popular Science Monthly/Volume 22/December 1882/The Cell-State
|←Brain-Weight and Brain-Power||Popular Science Monthly Volume 22 December 1882 (1882)
By Ferdinand Julius Cohn
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NOTHING is more sure than that all life is subject to age and death, and yet nothing is more contradictory to our feelings. In the vigor of youth our body feels as if it was created to last for ever; why must the highest work of art wear out and break down with time? The more formidable the contradiction between inexhaustible life-joy and inevitable fate, the greater the longing which reveals itself in the kingdom of poetry and in the self-created world of dreams hopes to banish the dark power of reality. The gods enjoy eternal youth, and the search for the means of securing it was one of the occupations of the heroes of mythology and the sages, as it was of real adventurers in the middle ages and more recent times. . . . But the fountain of youth has not been found, and can not be found if it is sought in any particular spot on the earth. Yet it is no fable, no dream-picture; it requires no adept to find it: it streams forth inexhaustible in all living nature. Nature continues eternally young; the earth adorns itself every spring with leaf and flower, having the same freshness and youthful vigor as when for the first time He "let it bring forth grass, the herb yielding seed, and the fruit-tree yielding fruit after his kind." The grasses and flowers, it is true, which this year are cut or withered, the leaves and blossoms which the wind has to-day blown from the trees, will not assist in forming its robe in the next spring, but Nature draws out new shoots from the old roots, new leaves from the old branches, and thus rejuvenates herself with every new year. And although the human race, although also the other kinds of animals and plants, show as yet no trace of age in spite of the numerous thousands of years in which they have dwelt on the earth, still each individual is perishable, it grows old and dies; but new generations shove themselves uninterruptedly into the gap, so that the whole abide in the freshness of youthful vigor. Rejuvenation so dwells in nature that every individual runs through a limited circle of development, and is finally worn out and cut off, to be replaced by fresh members which pass anew through the accomplished cycle.
If we apply this view which we have gained of the rejuvenation of nature to the consideration of a single being, whether it be man, animal, or plant, we shall perceive that all life rests upon a constant renewal. Life is an uninterrupted contest with death, which attacks it every moment, but is beaten back by rejuvenation. It would be an error to represent a living being as anything constant, its appearance as anything steady; life in truth resembles a water-fall, which only apparently preserves a constant form, while in reality none of the particles of water keep their places, but are continually removed and replaced by new ones. The visible form of stillness is kept up only in perpetual movement. Life resembles a flame, which restlessly consumes itself and can shed an even light only when new particles come up in place of those which have been burned, only to be dissipated in their turn a moment later. So in living bodies the combination and arrangement of the matter on which their outer form and internal disposition depend are at no two instants the same, but an uninterrupted change of matter is taking place. The particles which are together in this moment at one point are in the following moment separated and replaced by others. For only a short time are the atoms of which bodies are built up adapted to the service of life; sooner or later they leave it in order to follow the free play of the forces of attraction which join the elements in the enduring combinations of lifeless nature. Therefore, the living body is obliged constantly to take up from without new elements of nourishment, by means of which it repairs its loss; and these insinuate themselves so closely in the place of the separated ones, that even the eye of the naturalist, armed with the most effective aids supplied by modern science, has only recently remarked, after a long time, that any change has taken place.
In reality every living body is subject to an uninterrupted change, which goes on in an appointed course. Life is like a stream, which gushes out of a hidden spring; slowly increases, flows on for a time with even strength, finally with diminishing velocity, to disappear in the sea of eternity. We designate the course of changes which every living being, plant, and animal, as well as man, goes through, as its development. Development begins with the moment of birth and ends with death.
But with the death of the single being its race does not disappear; the property dwells in every living being by which a part of it can drop off from the whole, continue to develop itself independently, be nourished and rejuvenated by a change of matter. We call this dropping off of a part, capable of development, from the whole, propagation; with propagation is transferred the history of development; the separated part, which we denote as an egg or spore, a seed or embryo, a bud or spawn-knob, passes in substance through the same course of changes as the whole from which it has been separated. Like arises from like; the children resemble their parents, and, as these again resemble their ancestors, the character of the species is kept up essentially unchanged, in spite of the perishability of individuals, through all the generations.
That life is nothing but a constant development and an uninterrupted rejuvenation is expressed in the plainest and clearest manner in the world of plants. It is, indeed, not easy to comprehend the life of plants aright, and many regard the term as a figure of speech, not properly applied. Plants, they say, do not feel or move; they have no consciousness, no soul, like animals; how can we speak of their life? If motion, feeling, and consciousness alone constituted life, there might be some doubt as to whether plants lived, though it would still be worth while to inquire whether these higher attributes were really wanting in plants. Darwin has lately shown, in connection with many older observations, that all the parts of plants participate in a regular circling motion, and that single organs show sensibility enough to make them comparable with the brains of the lower animals. But when, instead of the highest acts of life, we confine ourselves to its general and essential manifestations, it becomes undoubtedly clear that plants are living in the same sense as animals and men. Only plants are distinguished, not from animals generally, but from the higher animals that rank nearest to men, and from which our conceptions of animal life in general have been formed, in that in them unity, or individuality, is expressed in a much more imperfect manner. The mammal, bird, fish, insect, is a separate, single, and indivisible being. Its members are fixed and limited in number; not one of them can perform its functions when separated from the whole. No part, not the smallest, can be separated from the body without the whole suffering.
It is very different with the plant. A tree indeed appears to be a single being, sinking the net-work of its roots into the ground, raising its slender trunk into the air and spreading out above the web of its limbs and boughs. The members of which the tree consists may be regarded as its organs. It sucks up its nourishment through its roots, it breathes through its leaves, it propagates its species through its flowers. But the connection of these members with each other is of an infinitely looser character than that of the organs of the animal. I can strip as many leaves as I please from a willow, the rest lives on; I can cut off its limbs, those that are left grow more vigorously; I can cut it down near the roots, new shoots spring up from the stump; I set the rootless stem in moist earth, and it continues to live. If I wish to make a layer, I have only to plant the end of a bough, and it takes root and grows. In many plants a single leaf has the capacity of living and growing. The plant is not therefore indivisible, like the animal; its individual members are in a much higher measure independent and competent to live. We may say the animal is a single being, each of its members is only a part, not itself a whole, only an organ, not itself an individual. The plant, on the other hand, is a composite being, a chain of individuals, each of which possesses an independent life, but all of which are connected in a collective life of a higher order; the plant is an organism the organs of which are themselves organisms.
This relation may be made clear by a suitable figure. A state is, without doubt, in many respects a single organism, which maintains an independent, often sharply denned, unchanged character through centuries, and marks its domain as an indivisible, also as a real individual. Each state has its own development-history: it is founded, it grows, reaches its prime, and decays; it has its life-economy, for the functions of which it maintains its particular organs, its officers. The state also acts in external affairs as a single organism; it makes war, it establishes enterprises for the general benefit, it builds important works, etc. But if the state thus appears as a single whole, so also it may be regarded on the other side as a collection of provinces; each province is a state in miniature, likewise organized in itself; and history furnishes us with numerous examples in which single provinces have been able to cut loose from the collective state and maintain themselves as independent state-organisms. The province, again, can be regarded as an association of villages which represent the smallest social organizations; every village is also a state in miniature, with independent economy, and capable of maintaining itself independently in case of necessity, and, in fact, of growing up, as Rome, Carthage, and Venice have shown, into mighty states. If we carry our similitude to the end, we may liken the animal to a compact, centralized, unitary state, the members of which have entirely lost their independence, and in which a single will rules the whole; while we may represent the plant as a freely organized federal state, the members of which, in spite of their resignation to the whole body, have yet preserved a certain degree of independence and self-administration.
In the federal state of the plant the limbs and boughs correspond to the provinces, the leaves to the villages; but the village is not the last member of the chain: it is itself a union of citizens, each one of whom, though a member of the state and the village, is an independent being who lives first for himself, and has his own household, all of whose efforts are first directed to the maintenance of his own existence. But while with a just egoism the citizen knows his own good as his immediate object, he thereby participates directly in the advancement of the state organism and contributes to the support of the whole state. Every citizen goes through his independent development from birth to death; but the village does not die with the death of the individual, for in his stead come his children to fill the vacant place; and the village and state are renewed in the unbroken succession of generations.
It is the same in the plant-state. If we compare the leaf with the village, it also consists of a larger or smaller number of individuals which may be regarded as independent organisms. The citizens, through the union of whom the plant-state is formed, are called by the botanist plant-cells. All plants, without exception, are composed in all their parts of cells, just as every building, from the palace to the hut, consists of building-stones or timbers. Every plant-cell pursues an individual life. Its first effort is only to maintain and develop itself; it takes its own nourishment and assimilates it, and finally dies, after having, as a rule, first left a posterity in its place. As the cells unite to form cell-villages in the leaves, these unite again to form the provinces of the foliage-boughs, and enter into an interchange of life with each other, and so they maintain the life of the whole plant in the same manner as the collective state-life comes into being through the interworking of the lives of the individual citizens. What we see going on in the life of the plant in the germ and shoot, in flower and fruit-bearing, are only head and state actions in the development of the cell-state and its citizens.
Our eyes can not perceive these citizens of the cell-state. It is not strange, then, that their existence escaped the knowledge of naturalists till about two hundred years ago. They would still be concealed, and the key to the comprehension of plant-life would be withheld from us, had it not been for the microscope.
We owe it to the microscope that, where the naked eye perceives only uniform masses, we can now distinguish a wonderful diversity of beautiful tissues; and that where a rigid stillness seemed to prevail, a fullness of life-processes quite incomprehensible to us is concealed. The microscope shows us in the plant, which was able to give to the naked eye only obscure signs of its inner life, a highly organized state life of restless development and renewal.
We have represented the citizen of this state, the plant-cell, as an exceedingly simply formed being: it consists of a round body of soft, slimy substance, like a sack, the interior of which is filled with a watery juice. The soft substance, forming the wall of the body, is called protoplasm; it is the most important matter in all nature, for it alone is the bearer of life. With slight changes it forms not only the bodies of all plant-cells, but also the white and yolk of the egg, flesh and blood, the substance of the brain and nerves, milk and cheese, the skin and hair of animals. While in lifeless nature nearly every kind of stone has a different chemical constitution, in the world of life one and the same fundamental substance forms the basis of the bodies of plants, animals, and men.
But if the plant-cell consisted simply of soft protoplasm, it would not be able to resist the presence and assault of strange bodies; therefore it is surrounded with a hard shell, which it prepares as a dwelling and for its protection, in a similar manner as the snail forms its shell, by secreting over its surface a matter which soon hardens into a firm, transparent envelope. This shell, which is called the cell-wall, does not show the most minute opening, but incloses the protoplasm perfectly tight. We might, therefore, liken the cell to an egg in which the soft, living contents are concealed in the hard shell.
Plant-cells vary greatly in size. Those of elder-pith and of the begonia-leaf may be perceived, with the naked eye, as resembling an extremely delicate lattice-work; the pollen of rye and of melons separates in water into little dust-particles—single cells, just at the limit of visibility. A drop of malt-yeast, on the other hand, is resolved under the microscope into millions of oval fungus-cells, one or two thousand of which would hardly fill the space of a centimetre. Plant-cells average about the size of a hair's-breadth, many only about a third or a fourth as much; others are larger, and particularly longer; the single fibers from which cotton and linen threads are spun are plant-cells which, although very slender, are from two to six centimetres long.
But in nature nothing is great and nothing little, and there is room, even in the smallest cell, for the greatest diversity and development of the powers of life. A continuous formation and transformation, origin and decay, a constant change of matter, is going on in every cell; reception and assimilation of food, inspiration and expiration; certain atoms which have become of no use for purposes of life are cast aside, others are taken up from without in their places; on this food and change of substance depend the renovation of the cell and the maintenance of its life. Evidently not solid substances are appropriated, for we know that the cell is incased in a perfectly closed envelope; but liquid and gaseous foods can be easily absorbed. Although the most perfect microscopes have never made any holes visible in the cell-envelope, there is not the slightest doubt that this envelope is porous, like a fungus, but that the pores are infinitely finer. Therefore, we may understand that, when a cell is placed in a fluid, the envelop absorbs it to fullness, and conveys to the inner protoplasmic body as much as it requires; and, inversely, certain parts of the cell-juices, which the living protoplasmic body does not need for itself, are transpired through the pores of the envelope and become applicable to the use of other cells; and the same may take place with air and gases.
The old naturalists believed that all bodies were composed of four elements—fire, water, air, and earth. Modern physics and chemistry have divested these elements of their high importance; but they are still full of meaning to the life of plants. Earth, air, and water are the food of plants; fire, or rather light and heat, are the forces that set agoing the play of life in the cells. The most important food of plants is contained in the mineral solutions which the water, penetrating the soil, extracts from it, and in the oxygen and carbonic acid which they derive from the air.
Water, earth salts, and the gases—the raw materials which the plants suck up—are changed within the cells into starch and sugar, gum and woody fiber., albumen and wax, oil and resin, into powerful medicines and deadly poisons. The simplest plant possesses an art which the most skillful chemist has not been able to learn from it. It is true that the chemist can artificially prepare in his laboratory many of the substances which the plant-cell likewise produces; he can convert the starch of the potato into the sugar that gives the wine-grape its sweetness; this, again, he can transform into the fruit-acids which, in connection with the sugar, give the berries their fresh and agreeable taste; he can even produce the flavor of the fruits from the fusel-oil which he obtains by the fermentation of the sugar. He can make the oil of bitter almonds from benzoic and formic acids; he can, with as good art, imitate the pungent taste of the pepper, and the biting one of the mustard-seed, and the narcotic poison which only the nightshade has hitherto prepared for the healing of sore eyes. He can produce from the sap of firs the crystal-needles of the vanilla, for which a Mexican orchid has heretofore been obliged to give up its pods; from the distillation of wood he obtains a smoky fluid, from which he procures salicylic acid, for the production of which the flowers of the meadow-sweet or the bark-tissues of the willow were formerly required; and from this he makes also the ink-coloring gallic acid, which formerly only a little wasp knew how to draw out by its sting from the cells of the oak, and the aroma of the wood-ruff. He has made the work of the cells in the madder-root superfluous, for he has fabricated its costly dyes, along with a hundred other splendid pigments, out of tar-oil and stone-coal; and is now on the point of taking its work away from the indigo-plant by artificially producing indigo. But a raw material which has at some time been brought forth out of the laboratory of a living plant-cell always lies at the foundation of all these manipulations of the chemist, wonderful as they are. And, notwithstanding the immense progress that modern chemistry has made within the last ten years, its art is still limited at this point: no prospect yet exists that it will be able, artificially, to produce the most important of all the substances that go to build up the bodies of animals and plants, and to form their living cell-tissues—protoplasm, or the envelope of the plant-cells, the matter of the muscles and nerves. Chemistry shares this limitation of its means with animals. No animal can live on air, water, and earth alone, like the plants; no animal can combine the simple chemical combinations, as they occur in lifeless nature, into the life-substance protoplasm. The animal must draw the substance of his flesh and blood from the plant, for his own vital forces are not competent to produce it. The plant-cells alone possess the faculty of ennobling the simple combinations of lifeless nature into matter fitted for life. Every cell, furthermore, possesses another art, that of forming different fabrics out of the same raw material. Hence arises that infinite diversity of substances of different properties which are drawn from the vegetable kingdom. Close together, in the shadow of the same wood, grow crow-foot and wood-ruff, centaury and nightshade; the same soil gives food to their roots, the same air plays around their foliage; and yet the cells of one secrete a pungent, those of another a narcotic poison, those of a third a bitter medicinal juice, those of a fourth an aromatic flavor. The cell utilizes a part of its food for its own growth; but, sooner or later, the growth ceases, and the cell, keeping the form and size it has acquired, becomes a permanent cell. It is round or oval, or resembles a many-sided crystal. Some cells become flat and square, like a tile; some put out rays, like a star, or form a zigzag, like the wall of a fortress; many lengthen themselves out. The inner structure, also, of the cell changes with age; the envelope, delicate and thin in youth, afterward receives accretions and ornaments. Some cells have within a hollow screw-way, like a winding stair; in others, the inside is covered with beautiful nettings, rings, flutings, or lattices. Most cells thicken their casings, as the oyster does, by adding new layers over the older ones; and, when their hollows are quite filled up, they may rival stones and bones in hardness, as, for example, the cells of the iron-wood and the ivory nut.
As the cell-wall grows thicker, fluids and gases penetrate its invisible pores with more difficulty; and with continuous increase of thickness the living protoplasmic bodies inhabiting its interior must finally die for want of food. They in effect build their own coffin, immure themselves living in their own cell-prison. But a wonderful provision prevents the food being entirely cut off. While the cell-wall is arching itself up more closely and thickly, a few doors and windows are still left open in it, through which communication may still take place with the adjoining cells; this occurs by the cell-wall not becoming strengthened at particular points; and when, in the course of time, the shell has become still thicker, these places appear as pores or canals, which lead outwardly from the interior of the cell. And it is worthy of remark that at each point where such a canal penetrates the thickened cell-wall a corresponding passage is also left open in the next cell, so that the two canals meet each other, and are only separated by a thin partition. Communication continues uninterrupted by these pore canals.
The plant-cell is, nevertheless, subject to the fate of all life— it grows old and dies at last. It seldom survives a summer; toward the end of the fall its activity becomes weaker. Dissolution gradually overcomes the dead protoplasmic bodies, and only the empty cell wall is left, which may continue to exist as a vacant chamber for years and centuries after the living nucleus has perished. As a rule, the cell propagates itself before it dies; as an earth-worm may be divided into two parts, each of which will become an independent individual, so the parent-cell divides itself into two daughter-cells, which supply the place of the mother, and continue their life-activity with renewed vigor.
Such in its principal features is the economy of the plant-cell. It is fed by the absorption of fluid and gaseous foods; it elaborates those foods into the most diversified products; it respires; it strengthens and thickens its shell, yet in such a manner that it can continue in living intercourse with its neighbors; it propagates itself by splitting into daughter-cells; it grows old and dies. Let us now glance at the arrangements and laws according to which the cells act in organic connection as citizens of a single state. As there are wild bees that do not live together in a hive, as there are human tribes that wander around in the woods without organic connection, so there are plant cells that remain isolated during all their lives; they all perform in the same manner the business of their whole existence, which is highly primitive, and unadapted to perfection; their progeny does not continue in social connection, but separates into wholly free individuals. Such plants, which always consist of single cells, are called one-celled; they are found among the lowest forms of the microscopic world, among the algae and the fungoids. The green coating that covers the rocks, the tree-trunks, and the shingles of the roof, is resolved by the microscope into innumerable green round cells; the brown scum that floats upon ponds and ditches exposed to the sun, the yeast-plant, the bacteria that produce putrefaction, are one-celled plants of this kind.
Generally, however, the plant-cell is, like man, a social being, which finds its true calling only in state-life. In most growths, from that of the moss to that of the oak-tree, an incredible number of cells come together to form an ordered state; the number of cells in a small plant may be compared with the number of the inhabitants in the most powerful kingdoms; and I have estimated that at least ten million cells live together in a potato five centimetres (about two inches) in diameter, and that a pine-stem twenty-five metres (about eighty feet) high and twenty-five centimetres (about one foot) in diameter, of symmetrical growth, contains more than a hundred milliard wood-cells.
The leading idea that knits the plant-cells into a state-organism is the same as in the bee-hive or the human state, the division of labor. Each cell possesses its individual life and passes through its particular course of development; it, however, does not undertake all the works of life, but limits the circle of its activities so as to reach a greater perfection within a smaller limit. In this it works not for itself alone but for the other cells also, while it commits to them those requirements for the satisfaction of which its individual activity is not sufficient. Thus the different functions are so divided among the different cells that one makes this, another that, occupation its own special business. The cells of the cell-state so arrange themselves in their different offices that they work mutually into each other's hands: one lives for all, all for one. The more perfectly the division is carried out, the more completely can each cell fulfill the duty for which it is designed; the more highly organized is the cell-state, and the higher position does the whole plant take in the order of growths.
As in the bee-hive there are working-bees, so in the cell-state of the plant there are working-cells; other cells are fitted for sexual existence, like the drones and the queen in the bee-hive, so as to insure the production of posterity and the foundation of a new stock.
The cells which discharge the several functions in the plant are not scattered confusedly in the mass, but are always grouped in greater or smaller numbers of individuals precisely adapted for this or that function, and together form a tissue. Plant-anatomists distinguish three kinds of tissues, each of which discharges a particular function: The fundamental tissue is composed of the cells which are the real workers in the state; the circulating tissue, of those cells on which the duty of transportation is laid; the bark-tissues, of those to which is assigned the protection of the cell-state against the outer world. We might designate as a fourth class the reproductive tissues, as including the cells adapted to propagation, which are producing by continuous divisions new colonies, new leaves and flowers, new buds and seeds.
The cell-state is, to speak with Herbert Spencer, organized after the type of an industrial state, in which numerous industrious workmen are co-operating on a footing of democratic equality to ennoble the raw material of lifeless nature and convert it into the precious and diversified productions of life. The fundamental tissue in a measure represents the working-class; trade is represented in the cells of the vascular tissue, which are engaged, by means of well-trodden routes of communication, in supplying the most remote parts of the domain quickly and abundantly with food and raw material and in exporting the finished fabric. But a defenseless kingdom would be an easy prey to its enemies; therefore the cell-state maintains, but peaceably, and with no view to aggression, in the cells of its bark-tissues, a standing army, on which depends the defense of the whole realm at its borders. As Sparta believed it was most securely defended by the living walls of its citizens, so does the cell-state. The cells of the bark-tissue form a close cordon, through which no rain-drops, no hurtful gas-puff, no hostile animal, no disease-generating spore can penetrate. They wear a hard, siliceous armor, or are protected by an impermeable coating of wax. They have no other purpose, they do no other work, than in compact array to ward off hostile attacks. Single cells advance before the line and oppose attacks with sharp-cutting weapons, finely pointed briers or thorns, or weave themselves into intricate abatis, in which hostile insects become entangled by their feet. The points of many of these thorns are poisonous, as in the nettle, which, when touched by the hand, breaks off and remains in the skin, and fills the invisible wound with one of the strongest poisons known to nature and science.
The cells of the bark-tissues are locked so closely to each other that, like the members of a brave phalanx, they would be torn apart before they would separate from each other; and they can be separated from the other tissues only as a connected layer, a thin membrane that may be drawn off from all plants, and is known as the epidermis. This living cell-fortification is interrupted in many places by round openings like gates, which may be closed by a couple of cells as if with double doors, by the opening of which the access and egress of gases and vapors to and from the interior are permitted.
Thus the plant is protected from external enemies; but its most dangerous adversaries are the hungry members of its own kingdom. Not all plants are supported by peaceful labors; there is among them also a predatory horde, whose members, the parasitical plants, unfit for honorable occupation, and bearing the marks of their baseness in their pale color and offensive smell, lurk in the darkness and in concealment till they can find some victim to attack and overcome. Now is the strength of the living wall of the plant tested: as long as it is unbroken, the assault is repelled; but the persistent enemy presses into the smallest opening. Woe to the tree from which the wind has broken a limb, or in which the careless gardener has made a bad cut! The microbes, whose spores are floating through the air in unwholesome clouds, and fall with the dust, settle upon the wounded surface, and soon its whole cell-structure is pervaded by their destructive webs.
In peaceful times the other citizens of the cell-state attend to their business undisturbed, under the protection of the bark-cells. The cells of the fundamental tissue, which is inhabited by the working people proper, unite in close association; between them courses, with numerous branches, a system of canals, which are connected with each other like net-work, and find their exit through the clefts. In this manner the air which they require for food and respiration is introduced to the cells, and by the same road escape the gases and vapors which the cells throw off, and which need to be removed.
The fluid foods are carried to the working-cells through the vascular tissue in a special system of ducts, conduits, and fibers, which, joined in strings and bundles, penetrate all the organs, the roots, stock, limbs, and leaves, and are known as the ducts, or vascular bundles; they may be most easily perceived in the leaves when held against the light, where they form the most beautiful vein-work. These conducting vessels are also traffic-roads, in which the products of the working cells of the main tissue are transported to other places, where they are put to use. Thus an unceasing activity, like that of the bee-hive, prevails in the cell-state of the plant. Gases go in and out; juices circulate up and down, absorption and evaporation, distillation and refining, forming anew, remodeling, or destroying the old, are going on all the time without rest or cessation for an instant. As long as the cells live, they are active; when they cease to work, their death is near. No one thinks, when he looks at a plant, what restless activity is at work within it, for the cells perform their artful labor in stillness, without buzzing and flying around as the bees do.
The wealth of those lands that possess coal-mines and ore-beds is highly prized. But these treasures are not confined to single provinces. Immense mines of ore, inexhaustible coal-beds, surround us wherever we may be. For the minerals that are contained in the field soils are quite as precious as are the mines of iron and zinc, yes, even of gold and silver. Man can not live on gold and silver; but out of the minerals of the field-soil, out of potash, lime, phosphoric acid, ammonia, and sulphuric acid, the cell-state of the plant prepares bread on which we live, linen in which we clothe ourselves, wood out of which we make our vessels and tools, and the remedies which when we are sick restore our lost health to us. The cells of the roots, like hewers and miners, sink numerous shafts in the spaces assigned to them, drive their galleries toward all points of the compass, in order to break up these mineral treasures, separate them from the incasing stone, and set the machinery of service in motion; day and night with inexhaustible diligence, they extract atom by atom of potash and ammonia, phosphoric and nitric acid, and, without working up their ore, deliver it over to the conducting vessels which transmit it by their powerful system of sucking and forcing pumps to the stem and the leaves. The leaves are cell-villages which perform their daily tasks in the air and the light. Their principal business is to obtain coal, which is the chief constituent of the vegetable body. Our atmosphere is an enormous coal-mine, many miles in thickness, that can not be exhausted in thousands of thousands of years. The coal, indeed, is not found pure in the air, any more than the metal in the ore, but is in combination with oxygen as a transparent gas, carbonic acid, and a peculiar art is required to separate it.
In the mining districts, smelting-houses are erected beside the pits, where the noble metal is extracted from the impure ores. The green cells of the leaves combine the art of the miner with that of the smelter, and have the power of extracting the pure carbon from the atmosphere. In order to perform this work, they must be shone upon by the sun, for the sunlight alone can excite in them the marvelous faculty. Having extracted the carbon, they combine it with water and with the mineral substances that have been drawn from the soil, and prepare from them the living matters out of which the plant itself builds up its cells, and which, taken up into the body of an animal, is transformed by it into flesh and blood.
As bees do not at once consume all the honey they collect, but lay away a large portion of it in special cells for winter provision, so a portion of the cells in the plant are set apart for the storage of capital in anticipation of the necessities of the future. On the approach of winter the leaves discharge the greater part of what they have produced through the conducting vessels, which convey it to a subterranean magazine. The cells of the root-stock, the tubers, and the bulbs, protected from the frost by their covering of earth, are filled with starch, albumen, and other valuable food-material, which will be used again in the coming spring when they will be most needed, for the expansion of the leaves and flower-buds. When we eat a potato, we appropriate to our own nourishment the provision which the careful mother-plant has laid up in its cells during the previous year for the growth of the next spring; and we do what is substantially the same as when in the fall we rob bees of a part of the honey which they have gathered for the supply of their own state.
A necessary consequence of the short duration of the life of the single cell is that a part of the plant, the cell-village, in which the life processes are now active, is generally dead in the next year, and unfit for all work. Therefore the cell-state is subject to a constant mortality. The leaves which perform their work in the summer wither and drop off in the fall; the cells of the root, also, which then drew up the fluids from the soil, and those of the stem, which conducted it upward, have at the same time grown old—have become woody, as the botanist expresses it.
The greater part of the plant does not, in fact, survive the first year. Most herbs sprout in the spring, blossom in the summer, ripen their seed in the fall, and perish in the winter. Trees, on the other hand, bushes and shrubs, possess a regular economical administration. They lay up, till fall, provision in their stems or roots, which does not come into use again until the next spring. And, when the collected capital enters into circulation again after the first warm days, the old cells are not able to undertake anew the business of turning it to use. The plant does not put its new wine into old bottles. It forms new cells, new organs, adapted to the demand of the new season. Now those tissues which we may call the procreative tissues come into play. Their cells begin to undergo a continuous division; their number is multiplied—new colonies, new cell-villages are founded. New points are formed at the ends of the roots, the young cells of which suck food from the soil with refreshed vigor; a new conducting tissue is formed in the stem between the wood and the bark, representing a new yearly ring. A grand act of renovation has also been in preparation at the ends of the limbs and twigs and at the bases of the leaves. Little cones of reproductive tissue are developed at these spots, in which innumerable cells originate by division, and, in accordance with an innate structural plan, a definite number of vesicles shoot in most symmetrical order of arrangement from each of these cones. Every cone is the beginning of a little stalk, the vesicles that grow from them are the beginnings of leaves; the whole structure is covered with thick scales and is now called a bud, in which the tender beginnings of leaves are protected by the scales from frost and storm. The buds are started in the summer, completed in the fall; are dormant during the winter, and are awakened to new life in the spring. The scale-armor now becomes superfluous, is cast aside; the little leaves rack and stretch themselves, and joyfully spread themselves out in the air and light; the little stalk grows longer and longer; in a little while the buds have shot out into young limbs, in the fresh foliage of which, excited by the light of the sun, the restless labor of the cells begins anew; or, after a marvelous transformation into flower-stalks, they produce those sexually developed procreative cells which are destined by a series of mysterious processes to found a new cell-state.
Thus is the cell-state of the plant subject to a continual rejuvenation. The individual citizens (the cells) and the villages (the leaves) have but a short life, but the state in its entirety may endure for centuries in lasting youth. If the hands of men, or the elements, do not inflict a violent death, the cell-state, as so many primitive giant trees have shown, may outlast the mightiest kingdoms of men.
Gifted writers on social politics have recently endeavored to illustrate the development and interrelations of human society by analogy with a living being and its cells. We have taken the converse course, and have endeavored to make the life of the plant and its cells comprehensible by a similitude with a state organization and its citizens. We have endeavored to show that what man has regarded as the highest ideal of his conscious effort in the struggles of the world's history has been prefigured in quiet accomplishment in the world of plants. It is the representative of the idea of the state which leaves its individual citizens to develop themselves freely according to their inborn natures, and to work together on an equal footing for the good of the whole; which preserves to the villages and the provinces their self-administration, and yet subjects them in every instant to the higher interests and laws of the whole; which appears ready armed against the external enemy, preserves unity and peace within; which applies the capital accumulated by the common labor of all the citizens to the advantage and advancement of the whole, without letting it be preyed upon by any; which in untiring activity never suffers a pause, and by continuous renovation endures for centuries, always increasing, always blossoming, and always bearing fruit.