Plant cell

“ Sometimes this new cell is needed to help do the work of a root, and so it begins to do this work, and becomes part of the root; or else it is needed to do stem work, and goes to make up the stem, or leaf work, and is turned over into the leaf.
A healthy cell is born with the power to do whatever is most needed.
HOW A PLANT’S FOOD IS COOKED Some time ago we learned that the little root hairs, by means of their acid, are able to make a sort of broth from the earthy materials which they could not swallow in a solid state. ”

“ All others, in which the grouping or modifications of the cell makes more complex structures, such as trees or shrubs and all the plants that grow, both flowering and flowerless, are called multicellular plants. Whether they be of one or many cells, these have the faculty of dividing, and by this division making two where one existed before the division. This division of cells is what happens in the normal growth of plants and it is this division, in more unusual ways, that results in the production of new plants without mating of the sexes. ”

“ It must always be remembered that plants are alive; their living matter is not in any way (so far as we know) essentially different from that of animals or of man. Their living matter (protoplasm) in leaf-stalks and leaves is cut up into boxes or cells, each enclosed in a case or wall of its own. Yet these are not entirely independent and unconnected, for thin living threads run from cell to cell, so that there is an uninterrupted chain of protoplasm all along the leaf, leaf-stalk, and stem. ”

“ In each cell we shall see signs of activity, the little round grains of chlorophyll are there, but instead of being stationary, as in the cabbage leaf, they are slowly moving round the walls of each cell. In reality they are carried along in the stream of living matter within the cell. It is a wonderful sight and brings home to the observer very forcibly a fact which is liable to be forgotten, that the plant is just as much a living being as an animal. Perhaps our experiment will not succeed at the first attempt, then we must try again ”

“ When we see the wonderfully varied forms of plant life, and yet learn that, so to speak, each edifice is built with the same kind of brick, called a cell, modified in form and function; when we see the smallest and simplest equally with the largest and most complicated plant increasing in size subject to the laws of growth by intussusception and cell division, which are universal in the organic world ”

“ By making a series of longitudinal sections with a sharp razor through the top of the plant, and magnifying sufficiently, it is found to end in a single, nearly hemispherical cell (Fig. 23, B, S) . This from its position is called the “apical cell,” and from it are derived all the tissues of the plant. Segments are cut off from its base, and these divide again into two by a wall parallel to the first. Of the two cells thus formed one undergoes no further division and forms the central cell of an internode (y) ; the other divides repeatedly, forming a node or joint (x) . ”

“ Each cell may be considered a distinct individual plant, since it is perfectly independent of others with which it may be aggregated, and performs for and by itself all the functions of growth and reproduction, having a containing membrane which absorbs liquids and gases from the surrounding matrix or elements, a contained fluid of peculiar character, formed out of these materials, and a number of excessively minute granules, equivalent to spores, or, as some would say, to cellular buds, which are to become the genus of new plants. ”

“ 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. ”

“ It passes through the stomata by diffusion, dissolves in the water, saturating the cell-walls, and so enters the cells. The organs by which the food is made are the minute, green bodies called chloroplasts or chlorophyll bodies, which give the plant its color. They are composed of protoplasm, which holds a green dye, chlorophyll, and are imbedded in the colorless protoplasm of those cells which lie near the surface of a plant. ”

“ This conception of the plant as an aggregate or colony of independent vital units governing the nutrition, growth and reproduction of the whole cannot, however, be maintained. It is true that in the unicellular plants all the vital activities are performed by a single cell, but in the multicellular plants there is a more or less highly developed differentiation of physiological activity giving rise to different tissues or groups of cells, each with a special function. The cell in such a division of labour cannot therefore be regarded as an independent unit. ”

“ In all Flowering Plants and in Conifers the male reproductive cells have no independent means of locomotion; they are carried to the female cell by the formation of a slender tube—the pollen-tube—produced by the pollen-grain. In the Ferns, Lycopods and Horsetails—in fact in all members of the Pteridophyta—as also in the Mosses and Liverworts as well as in many of the still lower plants, the male cells swim to the egg by the lashing of cilia like those on the male cells of Ginkgo. ”

“ Many of the lower plants are unicellular, as, for example, the common yeast-plant, bacteria, etc., among fungi, and the desmids and diatoms among algæ They increase in number by a simple division of the cell into two, each half increasing in size and dividing as did its parent. The individual among such plants is evidently the single cell. ”

“ They were not, and never became, wood cells, bark cells, pith cells, leaf cells or any of the other numerous, specialized kinds of cells which make up the plant world. They were something very close to the primaeval plant cells from which, in the course of a couple of billion years, all the others have been derived. Very early these unit structures of life learned that they must stick together and do specialized jobs for each other under the actual conditions of nature. Out of these combinations of specialists has arisen all the magnificent structure of the living world. ”

“ All plant-cells grow and divide at some time or other of their life; but whereas in a multicellular plant the products of division remain coherent, and add to the number of the cells of which the plant consists, in a unicellular plant they separate and constitute new individuals. In more highly organized plants vegetative propagation may be effected by the separation of the different parts of the body from each other, each such part developing the missing members and thus constituting a new individual. ”

“ The cells must turn a broad face to the outside; this they do by becoming arranged in branching rows, or in leaf-shaped flattened organs. That they may suck up water and salts from the soil, the cells are arranged as a highly branched system of roots, covered with delicate hairs, and penetrating the soil in every direction. To inhale the carbonic acid from the air, and to be subjected to the influence of sunlight, the aerial part of the plant stretches out its branches towards the light, and becomes folded into the flat leaves, the structure of which reveals a suitability for assimilation. ”

“ 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. ”

“ All insight not only into the chemical processes in the nutrition of plants, but also into the mechanical laws of the movement of the sap, and generally into the whole internal economy of plants, depends on a knowledge of the fact, that it is only the cells which contain chlorophyll, and therefore in the higher plants the leaves chiefly as consisting largely of such cells, which have the power of converting the gaseous food supplied by the atmosphere into the substance of the plant with the aid of the materials taken up from the soil. ”

“ The most important non-glandular synthetic tissue is the photosynthetic tissue, which is composed of the chlorophyll-bearing cells of the plant. These are the so-called green cells of leaves, of stems of herbs, of young woody stems, and in the older woody stems of plants like wild cherry, birch, etc. The greater part of the tissue of leaves is composed of chlorophyll-bearing cells.
Leaves collectively constitute the greatest synthetic manufacturing plant in the world, because the green cells of the leaf produce most of the food of men and animals. ”

“ Nothing whatever can pass into the cell-sap, or out from it, without traversing both the lining of living protoplasm and the cell-wall.
If we gently pull a living root, of wheat, pea, mustard, etc., from a normal soil, we find particles of soil so closely adherent to the root-hairs that they cannot all be washed off without tearing the hairs: the root-hairs establish relations of contact with these particles, so close that they are cemented to the solid surfaces by means of the gelatinous layer already referred to. ”

“ Receiving the water from the soil with such materials as it brings thence in solution, and absorbing carbonic dioxide and ammonia from the air, the living protoplasm of the leaf-cells has the power of chemically changing all these substances, and of producing from them those complicated and otherwise inimitable organic compounds of which the tissues of the plant are built up. ”

“ As, during all the stages of development, the tissues of plants consist of cells, and as new cells are not known to be formed between, or independently of, pre-existing cells, we must conclude that the gemmules derived from the foreign pollen do not become developed merely in contact with pre-existing cells, but actually penetrate the nascent cells of the mother-plant. ”

“ Cells of the outer skin of a leaf. At the bottom is the mouth of a breathing hole.
I have already said that at the time of year when the tree is growing rapidly, these woody cells are large; but when the tree is growing slowly, they are small. So each year there is a change from large cells formed in the spring to smaller ones grown in the fall. The next year, the living substance of the cell moves off to the growing region next the bark, and leaves the old wood cells empty. ”

“ Here the colorless cells—of the root, let us say—are bound to live at the expense of the green cells in the stem and leaves. Yet we do not think of this as a parasitic event. The root-cell is rather a unit in a vast colony of units (cells) associated for mutual benefit. The green cell gets quite as much good from the root-cell as the latter gets from the green cell ”

“ In any case we have here presented to us the strange and startling fact that the remarkable arrangement of protoplasmic matter and chlorophyll, which enables the vegetable cell to perform, with the aid of solar light, the miracle of decomposing carbon dioxide and water, and forming with them woody and corky tissues, had already been introduced upon the earth. It has been well said that no amount of study of inorganic nature would ever have enabled any one to anticipate the possibility of the construction of an apparatus having the chemical powers of the living vegetable cell. ”

“ The reason why these plants can live in such very [Pg 80] different regions is that they do not take their food through roots out of the ground, but suck in water and gases through the thin membrane which covers their cell, and each cell does its own work. So it matters very little to them where they lie, so long as they have moisture and sunlight to help them in their work. ”

“ In these cases, certain cells of a colony of unicellular plants or of the filaments of multicellular plants enlarge greatly and thicken their wall. When unfavourable external conditions supervene and the ordinary cells become atrophied, these cells persist and reproduce the plant with the return of more favourable conditions. ”

“ The living contents of young and active cells are mainly protoplasm with water or watery sap which this has imbibed. Old and effete cells are often empty of solid matter, containing only water with whatever may be dissolved in it, or air, according to the time and circumstances. All the various products which plants in general elaborate, or which particular plants specially elaborate, out of the common food which they derive from the soil and the air, are contained in the cells, and in the cells they are produced. ”

“ The tip of every twig is composed of minute cells endowed with a potentiality of development like that which characterises the embryonic tissues of a seedling just emerged from the seed. In the course of its growth, each branch, by means of its living and dividing cells, contributes to the several parts of the complex mechanism of the tree. While the greater number of cells acquire a permanent form and lose the « 9 » power of further development, there remains a cylinder of cells endowed with perpetual youth. ”

“ Having mentioned in a general way some of the wonderful powers of cells, it will be well now to describe briefly a few of the unicellular plants and animals that can be so easily obtained and studied in warm weather, and which may thus serve as illustrations of the powers of nucleated pieces of protoplasm or cells. Many unicellular plants and animals can be obtained in summer from the superficial ooze on the bottom of slow-running streams and also on the under surfaces of the leaves of water plants, a study of which will be of the greatest value and interest. ”