# Once a Week (magazine)/Series 1/Volume 11/The biography of a plant

THE BIOGRAPHY OF A PLANT.
When we compare human life with plant life it is astonishing to what an extent their vital phenomena resemble each other. All the stages of human life, of infancy, youth, manhood, and old age, are well-defined in plant life. About this there can be no mistake. The life of man compared with that of a plant! Are then the ties which unite us to plants so intimate? Yes! far more intimate than is commonly believed! To convince my readers of this, to strengthen their love of nature, and to make to them the plant-world more interesting, is my object in thus comparing our own life-changes with those of plants.
From the abundance which nature furnishes, we shall select—not a tree, for that sometimes outlives successive generations of men; besides, there is something strong, as well as enduring about a tree;—no! we must give the life-history of something in the vegetable kingdom far more frail and perishable; the biography, for example, of an annual plant, one of those flowers which adorn the garden or the landscape for a few months or weeks, and then pass away for ever, to be replaced by other floral forms as the seasons change, equally graceful, beautiful, and perishable.
The Stage of Infancy.—This commences with the first movement of re-awakening life in the seed, and closes with the fall of the cotyledons or nursing leaves. If we plant the seed of such an annual in a suitable soil when Spring and warm weather come it will begin to germinate, or its life-movements will re-commence. It first attracts the moisture from the soil to itself. This produces the softening and swelling of its outer covering, which is finally ruptured by the growth of the embryo in its interior, which sends downwards through the torn seed-cover a little rootlet, and upwards a young stem, to which are attached the first pair of leaves. These leaves, which are thick and fleshy, form the great bulk of the seed, and are called by botanists cotyledons: they are, in reality, the nursing leaves of the young embryo. We call them nursing leaves because they perform a duty quite peculiar to themselves, and therefore different to the work done by the other leaves which subsequently appear above them. They are thick and fleshy because they contain a store of starch, provisions elaborated by the parent plant which produced the seed, and whose last vital movements were expended in making this food for its offspring! On this store of starch, the infant plant, with its little root, and its stem bearing towards its summit the first true aerial leaves, is at first wholly parasitic, until it is sufficiently grown to attract from the earth and atmosphere a sufficiency of food for its support, and can do without the nursing leaves. It is quite obvious, therefore, that our plant must pass gradually from the stage of parasitism to that of independency.
During the first stages of its life, our little annual attracts oxygen from the air; this enters the nursing leaves, and through its influence, the starch which they contain is converted into a soluble sugary gum called dextrine, which the water absorbed during germination conveys to the rootlets in the soil, and to the young leaves forming in the atmosphere. Thus nourished, both grow, and the young leaves speedily expand and take the form peculiar to the plant.
With the progress of growth, the nursing leaves also undergo a great change in their appearance. Lifted above the ground and exposed to the light of the sun, they speedily expand and take a green leaf-like colour, becoming so much enlarged that they present quite a different appearance to that which they had when folded together and enveloped by the seed-skin. There can be no doubt that this change of colour enables them to discharge their nutritive duties more effectively. Now as the first rootlets and aerial leaves are formed principally out of the nutritive matter with which the cotyledons are furnished, they become gradually atrophied, or waste away and shrivel up, as the nutritious store in them disappears, and finally fall from off the stem. With the full development of the aerial leaves and the fall of the nursing leaves, the first stage of vegetable life, the stage of infancy, is closed.
It is thus that Nature, like an affectionate mother, cares for the life of all her plant-children, and gently weans them, first gradually altering their organism so as to adapt it to a change of diet, and then by degrees withdrawing the sustenance afforded by the nursing leaves. Surely, nothing can be more perfect or natural than this analogy between these early stages of plant life and those of human life!
The Stage of Youth.—This is the proper vegetable stage, throughout which the plant is wholly independent of the nursing leaves, and draws its nutritious material entirely from ​the earth and atmosphere, those two grand and inexhaustible store-houses of vegetable food. The commencement of this epoch is therefore marked by the atrophy and fall of the nursing leaves. See, how admirably the two extremities of our plant are organically adapted to the earth and atmosphere! A rootlet and a leaf, how different in form and colour! yet both are absorbents beautifully adapted to the two media into which they develope themselves. Their functions are the same. We cannot, in a paper like the present, undertake to enter minutely into the anatomy and physiology of these organs. Let it be remembered that this is only a brief outline of plant-life, sufficient to awaken, we hope, a pleasing train of thought in the mind of the reader. It is enough then if we simply state the facts. The little rootlets descend into the soil, and put forth from their surface innumerable fine white, hair-like fibres, which are the instruments by means of which the plant takes up its food; its young stem ascends into the air, and its bark and fibre, arranged cylindrically in separate beds or Layers in the stem, are spread out horizontally at definite points along its stem, in the form of numerous fiat, horizontal, green plates, or absorbent surfaces, called leaves. The bark or cellular tissue of these leaves is penetrated by the fibres of the wood in the shape of reins, veinlets and capillaries, which communicate directly with the fibres of the stem and roots, and thus act as conduits of the sap from one extremity of the plant to the other. In this manner the sap brought from all the other parts of the plant is conducted to all parts of the leaf by these veins, veinlets and capillaries, to be thoroughly spread out and aerated in the leaves.
The processes of evaporation and absorption are greatly facilitated by the organisation of the skin, or epidermal covering of the leaves. This skin, with its porous openings, is adapted to the aerial medium by which the leaves are surrounded. The porous openings are called stomata. They are, in fact, self-acting valves, and consist of two cells together, usually of an oval figure, with a slit in the middle. They are so situated as to open directly into the hollow chambers, or air cavities, in the interior of the leaf. It is through these pores that the superfluous water of the sap is evaporated, and such gases absorbed from the atmosphere as are nutritious to the plant.
The structure of the stomata, or pores, may be readily perceived on the epidermis of the lily, where they are unusually large. The epidermis must be carefully removed, and having been freed from its chlorophyl or leaf-green, it must be placed between two strips of glass, with a drop of water between them, so as to give it the necessary degree of transparency. Water ought, for this reason, always to be used, whenever objects selected from the tissues of vegetables are examined microscopically. The epidermis thus prepared will exhibit the pores, and the nature and beauty of their mechanism will be better understood and appreciated.
Hence, when fully formed, these aerial leaves aerate and elaborate the sap or nutritive fluid, in a much more perfect manner than the nursing leaves; and the growth of the plant is consequently more rapid after their evolution.
The leaves now contribute individually to each other’s support, the lower leaves aiding in the growth of those that are above them, and contributing also to the development of that portion of the stem which is below them, and to the increase of the number of rootlets in the soil, and thus vegetative power gradually increases. We have a manifest proof of this in the increase in size of the leaves from below upwards, and also in the increase in the length of the intern odes, or naked intervals of stem which separate them. For the size of the leaves and the length of their internodes depend wholly on the vegetative activity of the leaves themselves; and as those leaves situated towards the middle of the stem are not only larger, but more wide apart, than the leaves above and below them, it is evident that the growth of the plant is first accelerated and then retarded, and that the vegetative force is greatest about the middle of the stem. It is here, therefore, that the wave of growth culminates. From this point upwards the vegetative force diminishes, the leaves decrease in size, their internodes shorten, until finally the vegetative force is reduced to zero, and the leaves are crowded into those beautiful metamorphosed clusters, or rosettes, popularly called flowers. In the flower the wave of growth is depressed to a minimum, for when the flower appears, growth invariably ceases in that direction.
Our plant has now entered upon that interesting period which has been emphatically called “the change of life.” We notice a peculiar alteration in its habits and structure. Another force has come into play—that of reproduction —which gradually gains the ascendency, checks the growth of the plant, brings the leaves together, and finally culminates in the production of flower-buds. These differ only from leaf-buds in having no power of extension, for as in the flower the vegetative powers of the leaves are reduced to zero, the axis of the floral leaves necessarily retains its rudimentary ​condition, and no intervals of stem whatever are formed between them. The vegetative stage of youth is passed away for ever, and the plant has now entered upon the reproductive period of its life, or the
Period of Puberty.—This epoch in plant life clearly corresponds to the same interesting and critical period in human life, when man attains his greatest strength, and woman is most gentle, graceful, beautiful. “All flesh is as grass, and all the goodliness thereof is as the flower of the field.” Isaiah xl. 6.
In the flower the leaves are crowded together in order that they may communicate in a peculiar manner with each other, and in consequence of the gradual expiration of the vegetative force in that direction. Hence the change of structure or departure from the ordinary type of leaf increases as we pass from the outside to the inside of the flower; for the vegetative forces are gradually enfeebled in the flower, and reduced to zero in the centre, where the metamorphosis of the leaf is at a maximum, or the leaf attains its highest stage of organic perfection.
We select for analysis one of the more highly organised flowers, where all the parts usually described are present. We must however say that these parts, though well defined in some flowers, are more or less blended together in others. Nature laughs at all such distinctions, and we seek in vain to confine her within the fetters of an artificial nomenclature. The following distinction of parts, is, however, very convenient for beginners. The flower, then, consists of four sets of progressively metamorphosed leaves. The two outer sets which are generally the most showy, are simply the envelopes which surround the true botanical flower. They are called the calyx and corolla. Let us consider each.
The Calyx.—This, when well-defined, constitutes the outermost cluster of the floral leaves. Although greatly diminished in size, the leaves of the calyx not unfrequently retain their green colour. Individually they are called sepals (lat. sepalum, a leaf), collectively the calyx (gr. κάλυξ, a cup), because they form a cup-like involucre around the next set of leaves, which are called collectively
The Corolla (lat. corolla, a garland), and individually petals (πέταλον, a leaf). These are the most showy leaves in the cluster, constituting the part which is popularly considered as the flower. Thus the red petals of the rose, the yellow petals of the butter-cup, the white petals of the lily, constitute the corolla of those plants.
The Stamens.—These are situated immediately within the corolla. In the stamen the stalk of the leaf is converted into a filament, and the delicate portion or blade into a club-like body called an anther. This anther consists of two lobes or cells, which correspond to either side of the lamina leaf-blade, and lying between them you will notice a prolongation of the filament called the connectivum or connective, which answers to the middle of the leaf. The inside of the anther is filled with fertilising matter called pollen. The stamens are called collectively the Andrœcium (ἀνὴρ, a man, οἶκος, habitation).
The Pistil.—This consists of a leaf folded on its midrib, the two sides of the lamina or blade of which are united at their margins to form the ovary. The summit of this folded leaf denuded of its epidermis corresponds to the stigma of the pistil. The interjacent portion between the ovary and stigma is called the style. The pistils are always situated in the centre of the flower; when both stamens and pistils are present in the same flower the former always surround the latter. The ovary of the pistil is so named, because it contains the ovules, which after fertilisation are transformed into seed.
The process of fertilisation.—This takes place when all the floral leaves have arrived at maturity, and is as follows :—
When the flower is fully expanded, at first the anthers of the stamens are unruptured, moist, and closed; but, as the stamens approach maturity, the anthers become dry, open their cells, and discharge their pollen on the stigmatic surface of the pistils, which about this time exudes a clammy fluid which serves to retain the pollen-grains. These grains absorb the exuded fluid, swell out, and finally emit delicate tubes, which penetrate the loose cellular tissue of the style, and convey the fertilising fluid contents of the pollen-grains to the ovules in the ovary of the pistil. The ovules having received the impregnating matter, the embryos or miniature-plants begin to form in them, and the ovules are then gradually transformed into seed. With the discharge of the pollen, the act of fertilisation is accomplished. The vital forces from this period begin to be enfeebled, and all the phenomena mark another well-marked change in plant life, a gradual subsiding of all energetic life movements, which culminates in death and disorganisation. Our plant therefore clearly enters upon
The Period of Old Age.—In all the previous stages of its existence it was a beautiful subject for contemplation, but it is particularly interesting as a study when it approaches the close of its allotted period of life. What! when its leaves are withering and falling from its stem, when its flowers are losing their brilliant hues and inimitable colouring, and when ​the whole vegetative economy is languishing? Yes, even then it becomes, if possible, an object of deeper admiration! Why do the flowers lose their beauty, the petals detach themselves and fall, the stamens experience the same degradation, the stigmas and styles of the pistils disappear equally with the other parts? It is because these parts have done the work which was assigned them by nature; and also, for this reason, a new vitality has now been established in the impregnated parts to their detriment. Take, as an example, the forming pod of the common garden pea, which everybody knows makes its appearance after the flowers have faded and fallen. That pod is the ovary of a pistil. The calyx will be found at the bottom of that pod, and at its top the remains of the style and stigma. Its two surfaces are at first flat and parallel with each other, but as the ovules in its interior grow in size, they become convex. The sap from the leaves now passes through what was formerly the peduncle or flower-stalk into the green walls of this pod or ovary, which acts like a leaf on the atmosphere, and having been rendered there additionally nutritious, the currents finally meet and pour their contents together into the little cord of vessels, or seed-stalk, which attaches the ovule, or forming seed, to the maternal wall of the ovary, and which may be very properly called the umbilical cord, or vegetable navel-string. The currents of sap are all converging to those little seed-stalks, to those forming plant embryos contained in the seed, and the little store of starch is being prepared which is to support their infant-life. Nature carries on this process until the embryos, their food, and the wrappers, or seed-covers, are all perfected, the transformation of the ovule into the seed is then accomplished, and all the movements of life cease.
We must add that the seed-vessel as it matures always assumes such an organisation as is calculated to effect the dispersion of the seed which has been thus brought to maturity. Sometimes the seed-vessel opens with a spring-like mechanism, as in the furze-bush and garden balsam, and the seeds are projected to a considerable distance from the plant. Who has not seen the wind performing its duties as a faithful servant of Nature, and transporting the seeds of the willow-herb and dandelion from their parent plants? The beautiful stellate down attached to those seeds—what is this but a contrivance catch the breeze? Here we must stop. We are entering a new and vast field where Nature displays her usual provident care. If any of the innumerable seeds thus scattered abroad find a suitable home, all is quiet until the return of the proper conditions of temperature, air, and moisture, when our little friend wakes up, re-appears on the earth’s surface, running through precisely the same instructive and ever deeply interesting life-movements. And we must add, in conclusion, we are always glad to see our little friend, to whom we are becoming every season increasingly attached.
Harland Coultas.