Chlorophyll

“ The great majority of conspicuous plants are, as everybody knows, green; and this arises from the abundance of their chlorophyll. The few which contain no chlorophyll and are colourless, are unable to extract the carbon which they require from atmospheric carbonic acid, and lead a parasitic existence upon other plants; but it by no means follows, often as the statement has been repeated, that the manufacturing power of plants depends on their chlorophyll, and its interaction with the rays of the sun. ”

“ The action of chlorophyll in the life of a plant is important, as it breaks up the carbonic acid gas taken in by the plant into its two elements, oxygen and carbon, converting the carbon with the water in the plant into starch, and giving back the oxygen to the air. Light is indispensable for the production of chlorophyll; without light plants become bleached or etiolated, a circumstance utilized by the gardener to produce a blanched appearance on certain vegetables. ”

“ On this physiological basis “soil-algæ” may be defined as those micro-organisms of the soil which have the power, [100] under suitable conditions, to produce chlorophyll. Such a definition has the advantage that it is wide enough to include the filamentous protonema of mosses, which, though alga-like in form and in physiological action, is nevertheless separated from the true algæ by a wide gulf. A more accurate name for such a group of organisms would be the “chlorophyll-bearing protophyta” of the soil ”

“ Chlorophyll grains lie just behind the skin cells in all parts of the plant that look green. The cells they lie in are often long with their short ends towards the skin. Leaves contain several layers of chlorophyll cells. The inner ones are not long like the outer ones, and do not contain so many chlorophyll grains. In the illustration, a, a represent the upper and lower skin and b the cells containing chlorophyll. The under side of a leaf usually has fewer chlorophyll grains in its cells, for the light is not so bright there, and chlorophyll needs plenty of light. ”

“ Without it all except a very few plants would die, and even in those beautifully colored leaves like coleus or caladium chlorophyll is always found, but in these colored leaves it is merely obscured by other coloring substances. It is in the chlorophyll that the ability resides to take the inorganic substances through the roots or from the air, and by the aid of sunlight transform them into organic substances like starch and sugar. Nothing else in all nature can do it; without this faculty, which the commonest green leaf possesses, the earth would prove uninhabitable within a single year. ”

“ An honest herb abounds in good green coloring matter (chlorophyll) , that serves as a light screen to the cellular juices of leaf and stem. It also forms part of its digestive apparatus, aiding a plant in the manufacture of its own food out of the soil, water, and gases; whereas a plant that lives by piracy - a parasite - or a saprophyte, that sucks up the already assimilated products of another's decay, loses its useless chlorophyll as surely as if it had been kept in a cellar. In time its equally useless leaves dwindle to bracts, or disappear. Nature wastes no energy. ”

“ One cannot help being struck with the fact that green is the prevailing colour among plants and the reason is not far to seek. If we take a cabbage leaf and carefully tear off the skin, we shall find green [98] spongy matter below. A little of this green material may be examined under the microscope and will show us rounded green bodies composed of a substance called chlorophyll. Now chlorophyll is absolutely necessary to all plants, except the fungi and to one or two parasitic plants. ”

“ An ample pipe-system extends from root, through stem, to leaf, but it does not communicate directly with the openings at either end. All material, whether liquid or gaseous, absorbed or given out, has to run the gauntlet of the living cells, which are jealous watchmen, and allow only selected substances to pass through them. The crude building materials and food materials are assembled in the leaves, where in cells spread out to the light the chlorophyll is massed. Under the microscope, the chlorophyll is seen to be located in minute granules embedded in the semifluid contents of the cells. ”

“ Decomposition of the Chlorophylls by Alkalies.—The first action of dilute alkalies on the chlorophylls is to split off, by hydrolysis, the alcoholic groups of the esters, producing the crystalline tri-basic acids, or chlorophyllins a and b. Each of these chlorophyllins exists in two forms, the normal and the iso, in which the attachment of the COOH groups to the other groups in the molecule is in different positions. Hence, chlorophyll a yields chlorophyllin a and isochlorophyllin a, and chlorophyll b yields chlorophyllin b and isochlorophyllin b, all four of which are tri-basic acids. ”

“ Plants get water (H2O) from the earth and carbon dioxid (CO2) from the air. When the sun shines on chlorophyll, the green substance in plants, the chlorophyll puts them together and makes sugar. The plant changes this sugar into starch and other foods, and into the tissues of the plant itself. Nothing in the world can put carbon dioxid and water together and make food out of them except certain bacteria and the chlorophyll of plants. And light is absolutely necessary for this chemical action. Try this experiment:
Experiment 102. ”

“ With a higher power, each cell (Fig. 11, A) is seen to have a distinct cell wall, within which is colorless protoplasm. Careful examination shows that the chlorophyll is confined to several roundish bodies that are not usually in immediate contact with the wall of the cell. These green masses are called chlorophyll bodies (chloroplasts) . Toward the centre of the cell, especially if it has first been treated with iodine, the nucleus may be found. The size of the cells, as well as the number of chloroplasts, varies a good deal. ”

“ If, however, the chlorophyll and the leaf containing it are exposed to a light of such intensity that the chlorophyll is decomposed faster than it can be rebuilt, then damage must ensue, which if sufficiently extensive will result in the death of the entire leaf. The intensity of the light which induces a maximum of activity in any plant, and which it may receive without damage, is determined by its specific constitution. ”

“ These facts premised, we are in a position to follow generally the astounding transformations which go on in these millions of chlorophyll corpuscles in the oak-leaf. Carbon dioxide and water exist side by side in the protoplasm of the chlorophyll corpuscle, and rays of sunlight—i.e., energetic vibrations of the ether which pervades the universe—penetrate into the system. ”

“ The absence of color is an index of parasitic or saprophytic life, but it must be borne in mind that many parasites and saprophytes are highly colored. The most common coloring matter in plants is chlorophyll, which manifests itself in various shades of green. Light of some strength has been shown to be necessary for the development of chlorophyll, though recent experiments show that it may develop in various seedlings germinated in perfect darkness, and that the synthesis of carbohydrates may take place vigorously under a dense layer of cork. ”

“ It exists in the cells of plants in the form of granules, and is intimately associated with the living matter or ‘protoplasm’ of the cells. The presence or absence of green colour in a plant makes all the difference in the world to its habits. The want of this chlorophyll, in fact, converts the habits of the plant into that of the animal. ”

“ Green plants—those containing chlorophyll— manufacture their own starch from CO2 and H2O. These chlorophyll grains are the plant's chemical laboratories, and hundreds of thousands of them exist in every leaf. CO2 and a very little H2O enter the leaf from the air, H2O being also drawn up through the root and stem from the earth. In some unknown way in the leaf, light has the power of synthesizing these into starch and setting free O, which is returned to the atmosphere.6 CO2 + 5 H2O = C6H10O5 + 12 O. As no such change takes place in darkness, all green plants must have light. ”

“ Typical plants have chlorophyll; they are able to feed at a low chemical level on air, water, and salts, using the energy of the sunlight in their photosynthesis. They have their cells boxed in by cellulose walls, so that their opportunities for motility are greatly restricted. They manufacture much more nutritive material than they need, and live far below their income. They have no ready way of getting rid of any nitrogenous waste matter that they may form, and this probably helps to keep them sluggish. ”

“ The combination of carbon with water carried out by the agency of chlorophyll can only take place with absorption of energy. This energy comes directly from the sun, the red and orange light radiations being absorbed by the chlorophyll. {11}The arrest of vegetation during the winter months is due not so much to the lowering of temperature as to the diminution of the radiant energy received from the sun. In the same way shade is harmful to vegetation, since the radiant energy required for growth is prevented from reaching the plant. ”

“ The energy thus gained is partly used in the making of new foods (see Photosynthesis) . In the absence of chlorophyll, this work cannot be accomplished. Chlorophyll is probably being continuously produced and destroyed in green plants. It is not usually formed in darkness, and if light is excluded from a green plant the destruction of the chlorophyll leaves it a pale yellow. Autumnal colors are due in part to the decomposition of the chlorophyll. ”

“ The chlorophyll grains attract carbon dioxide as strongly as a magnet attracts bits of iron. The carbon dioxide in the air goes through the pores in the leaf skin, right through everything to the cell where the chlorophyll lies. You know carbon dioxide is made of carbon and oxygen. The plant needs a great deal of carbon, for nearly all its hard parts are made of it. Wood for one thing is nearly all carbon. ”

“ My older readers know, of course, that the green color of the leaf is due to the numerous corpuscles of chlorophyll which fill the cells. This same chlorophyll has an important mission to fulfill. These little green bodies are the only real food-making machines in nature. Upon the product of these tiny mills all animate nature depends for food. Their motive power is light, and their raw material the inorganic fluids absorbed by the roots from the soil, and their product is sugars and starches. ”

“ The constructive photosynthetic processes of green plants are regulated and controlled by a pigment, chlorophyll, which is almost identical with the blood pigment, hæmatin", which regulates the vital activities in the animal organism, differing from the latter only in the mineral element which links the characteristic structural units together in the molecule. Many other points of similarity in the chemistry of the life processes of plants and animals will become apparent as the study progresses. ”

“ Chlorophyll is dependent upon the action of light, if not for its formation, at all events for its development. Keep a plant in a dark room or cellar, and it will become blanched [369] and sickly; the colouring matter dries up, and the white, wan tissue of the leaf is all that survives. The more a plant is exposed to the light, the deeper will be its green. In a shrubbery you may notice that the brown leaves of any particular ever-green or bush, if so situated as to lose the direct action of the sun's rays, will soon change colour. ”

“ The colouring of plants is neither so varied nor so complex as that of animals, and its explanation accordingly offers fewer difficulties. The colours of foliage are, comparatively, little varied, and can be traced in almost all cases to a special pigment termed chlorophyll, to which is due the general green colour of leaves; but the recent investigations of Mr. Sorby and others have shown that chlorophyll is not a simple green pigment, but that it really consists of at least seven distinct substances, varying in colour from blue to yellow and orange. ”

“ In order that they may perform their functions properly, however, it is essential that they be exposed to light; this is effected by their being in cells which are disposed in thin layers, such as we have seen the mesophyll of the leaf to be. In fact, the flat, thin, expanded form of the leaf is a direct adaptation to the end that these chlorophyll corpuscles shall be properly illuminated by the sunlight ”

“ When the oxygen flies away into the air again and leaves the carbon behind, the work of the chlorophyll has but just begun. Raw carbon is of no use whatever,—no more use than carbon dioxide, which we know is good for nothing to the plant or else the chlorophyll would not tear it to pieces. ”

“ In by far the greater number of plants the protoplasm of most of the cells which are exposed to the sunlight undergoes a curious and important differentiation, part of it becoming separated from the remainder in the form usually of green granules, known as chlorophyll. The chlorophyl-granules thus consist of true protoplasm, their color being due to the presence of a green coloring matter, which may be extracted, leaving behind the colorless protoplasmic base. ”

“ Strictly speaking, only those plants whose every cell contains chlorophyll are entirely self-nourishing; and some parts, or organs, of almost any autotrophic plant are dependent upon the active green cells of other parts of the plant for their synergic food. Furthermore, if the term is used in a very wide sense, green plants are more than self-nourishing, they really nourish all living things. ”