VEGETATION AND THE ATMOSPHERE

Field, Forest and Farm by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. VEGETATION AND THE ATMOSPHERE

CHAPTER VIII. VEGETATION AND THE ATMOSPHERE

“The carbonic acid gas produced simply by the breathing of the great human family amounts every year to about 160,000,000,000 cubic meters, which represents 86,270,000,000 kilograms of burnt carbon. Piled up, this carbon would form a mountain one league round at its base and between four hundred and five hundred meters high. So much carbon is required by man to maintain his natural heat. All of us together eat this mountain of carbon in our food and in the course of the year dissipate it all in the air, a breathful at a time; after which we immediately begin the dissipation of another mountain of carbon. How many mountains of carbon, then, since the world was created, must mankind have exhaled into the atmosphere!

“We must take account, too, of the animals, which, collectively, those of the land and those of the sea, use up a big mountain of combustible matter. They are much more numerous than we; they inhabit the entire globe, both continents and seas. What a quantity of carbon it must take to sustain the life of our planet! And to think that it all goes forth into the air, as a deadly gas, of which a few breaths would cause death!

“Nor is that all. Fermentation, as in grape-juice [43]and rising dough, and putrefaction, as in decaying manure, produce carbonic acid gas. And it needs only a light layer of manure to cause a cultivated field to give forth between one hundred and two hundred cubic meters of carbonic acid gas per day for each hectare.

“The wood, coal, and charcoal burnt in our houses, and especially the quantities consumed in the great furnaces of factories—are not they also returned to the atmosphere in the form of harmful gas? Just think of the amount of carbonic acid gas vomited into the atmosphere by a factory furnace into which coal is poured by the carload! Think also of the volcanoes, gigantic natural chimneys which in a single eruption throw up such quantities of gas that furnaces offer no comparison. It is very clear: the atmosphere is constantly receiving carbonic acid gas in torrents that defy computation. And yet animal life has nothing to fear for the present or for the future, since the atmosphere, though continually being poisoned with carbonic acid gas, is at the same time always being purged of it.

“And what is the purgative agent commissioned by Providence to maintain the salubrity of the atmosphere? It is vegetation, my friends, vegetation, which feeds on carbonic acid gas to prevent our perishing and turns it into the bread of life for our sustenance. This deadly gas, which absorbs into itself all sorts of putrefaction, is the choicest of nourishment for plant-life; and thus out of the bosom of death the blade of grass builds up new life.[44]

“A leaf is riddled with an infinite number of excessively minute orifices, each encircled by two lips which give it the appearance of a half-open mouth. They are called stomata. On a single leaf of the linden more than a million can be counted, but so small are they as to be quite invisible without a magnifying-glass. This picture shows you how they look under a microscope. Well, through these orifices the plant breathes, not pure air such as we breathe, but poisoned air, fatal to an animal but wholesome for a plant. It inhales through its myriads of millions of stomata the carbonic acid gas diffused through the atmosphere; it admits this gas into the inner substance of its leaves, and there, under the sun’s rays, a marvelous process follows. Stimulated by the light, the leaves operate upon the deadly gas and take from it all its carbon. They unburn (the word is not in the dictionary, more’s the pity, for it gives the right idea)—they unburn the burnt carbon, undo what combustion had done, separate the carbon from the air with which it is bound up; in a word, they decompose the carbonic acid gas.

Stomata on a Linden Leaf

“And do not think it any easy thing to unburn a burnt substance, to restore to their original condition two substances united by fire. Scientists would need [45]all the ingenious means and powerful drugs they possess to extract carbon from carbonic acid gas. This task, which would tax the utmost resources of the man of science, leaves accomplish noiselessly, without effort, even instantaneously, and with the sole requirement that they shall have the aid of the sun.

“But if sunlight fails, the plant can do nothing with the carbonic acid gas, the chief item in its diet. It then pines away with hunger, shoots up as if in quest of the missing sunshine, while its bark and leaves turn pale and lose their green color. Finally it dies. This sickly state induced by the absence of light is called etiolation. It is artificially produced in gardening for the purpose of obtaining tenderer vegetables and of lessening or even entirely removing the too strong and unpleasant taste of some plants. In this way some salad greens are bound with a rush so that the heart, deprived of the sun’s rays, may become tender and white; and thus, too, celery is banked up and left to whiten, since otherwise its taste would be unbearable. If we cover grass with a tile or hide a plant under a pot turned upside down, we shall after a few days of this enforced darkness find the foliage all sickly and yellow.

“When, on the other hand, the plant receives the sun’s rays without hindrance, the carbonic acid gas is decomposed in no time, the carbon and the air separate, and each resumes its original properties. Freed of its carbon, the air becomes what it was before this admixture: it becomes pure air, fit to maintain [46]both fire and life. In this state it is restored to the atmosphere by the stomata to be used again in combustion and respiration. It entered the plant as a fatal gas, it leaves it as a vivifying gas. It will return some day with a new charge of carbon, which it will deposit in the plant, and then, restored to purity once more, it will recommence its atmospheric round. A swarm of bees goes and comes, from the hive to the fields and from the fields to the hives, on one trip lightened and eager for booty and on the other heavily laden with honey and returning to the comb on wearied wing. In the same way air on coming to the leaves is charged with carbon from an animal’s body, a burning fire-brand, or decaying matter; it gives it to the plant and departs for a fresh supply.

“It is thus that the atmosphere preserves its salubrity despite the immense torrents of carbonic acid that are cast into it. The plant lives on deadly gas. Under the action of the sun’s light it decomposes the gas into carbon, which it keeps for building up its own substance, and breathable air, which it returns to the atmosphere. From this carbon combined with other substances come wood, sugar, starch, flour, gum, resin, oil, in fact every kind of vegetable product. Animal and plant are of mutual assistance, the animal producing carbonic acid gas, which nourishes the plant, and the plant changing this deadly gas into air fit to breathe and into food. Thus our dependence on plants is twofold: they purify the atmosphere and they give us food.”[47]

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