This section is from the book "The Gardener's Monthly And Horticulturist V26", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
One of the most important discoveries and generalizations of modern times, is the fact that all organic beings, in all their parts, are composed of small, and in many cases, of infinitessimal vesicles in the form of minute sacks, or tubes, termed organic cells. This discovery is one of the many important results of the invention of the microscope, by the aid of which we have become acquainted with myriads of wonders beyond the reach of our unaided vision. No study of the grand and imposing is of more interest than is that of the indefinitely small in the vegetable and animal kingdoms. The organic structure of the vegetable world is composed of a great variety of different structures that can be determined only by he aid of a high magnifying power. If we inquire in regard to the ultimate analysis of these we learn that they are composed almost wholly of carbon, hydrogen, nitrogen and oxygen. They also contain minute portions of earthy and saline matters. The combination of these elements so as to form organic substances can take place only under the action of the life force or vital principle.
No knowledge of the nature of matter and forces of nature, united with the utmost skill in their manipulation, has ever enabled the chemist to build up a particle of living organic matter from non-living matter. This is the office of life, and so far in the world's history, its domain, in this respect, has not been invaded by any other force or power in nature. All vegetable structure has its foundation in the vegetable cell, as to both the time and form of its organization. Before proceeding to investigate the form and function of the cell, it may be well to inquire in regard to the dimensions it attains, so that we may be better able to form a correct estimate of the object with which we have to deal. The size of cells varies greatly in different substances and in the different parts of the same object. In the pollen of flowering plants they are less than one-thousandth of an inch in diameter, while in the orange and lemon they often measure one-fourth inch in length. There is a creeping marine plant, the Caulerpa prolifera, the whole plant of which consists of a single cell, although it has the appearance of having stems, leaves and roots. Each fiber of cotton consists of a single elongated cell.
In the lower orders of plants, as in Fungi and Algae, are many unicellular plants, and in many others the cells are but loosely attached to each other. The spores of most cryptogamic plants are single cells, many of them being microscopic in size, while others are visible to the naked eye. The form of cells is determined largely by surroundings. As a rule, in the loose and fleshy parts they are globular in form and only touch each other, leaving spaces between them called intercellular spaces. These are sometimes filled with air and at others with water. Where there is a uniform and moderate pressure on all sides the cells assume the form of adodecahedron, as every cell touches twelve others. When the pressure is unequal in different directions, the cell is often elongated in the direction of the least pressure, as is the case in the stems and hairs of plants. But in some water plants the cells assume a stellar form. In the wood and bast or inner bark of trees and plants, they become much elongated. The wood cells are cylindrical, tapering to the ends, and so arranged as to overlap or break joints. Bast cells are generally long and slender, and in some cases very tough. The bast fibers of flax, hemp, agave, jute, etc, are examples of remarkable elasticity, flexibility and toughness.
The fiber of flax is more elastic, and that of cotton more flexible, because the former has thicker walls and retains the cylindrical form, but the latter when free from water collapses and assumes the character of a twisted, flexible strap. When the intercellular spaces are so arranged one above the other as to correspond for some distance, they form intercellular channels or passages, and if many of them unite at one point, large open spaces are formed called lacunae. Large open cells are often placed end to end so as to form interrupted passages separated by septa, which disappear by absorption, thus forming continuous passages called ducts. These are named from peculiarities in form of construction or the purpose they serve in the vegetable economy. In one style there is a deposit of matter in circular rings at regular intervals on the inside of the ducts; hence these are termed annular or ring ducts. In others a fiber of similar matter is wound in a spiral from one end to the other of the duct forming spiral ducts. Others have numerous pits or punctures, leaving thin spots in the cell wall, and hence are termed pitted or dotted ducts. Some plants are furnished with ducts whose office is to secrete a milky fluid, as in the milk weed, dandelion and sweet potato.
These are called milk ducts. A combination or aggregation of cells forms a tissue named according to the kind of cells and the mode of their combination. Thus we have vascular tissue, bast tissue, cellular tissue, woody tissue. Let us now take up the individual cell and see what we can learn of its construction and functions. If we take a cell from the growing part of a plant, as of cabbage, artichoke or potato, it will be found to be of a globular, sexagonal or dodecahedral form. On the outside is a thin wall or partition composed principally of cellulose, a substance that in its chemical constituents is precisely similar to starch. Inside of this is a thin lining membrane that has been found to consist of a viscid albuminous matter. This has been termed protoplasm or the formative layer, because it is the first part of a cell that is formed, all other parts being formed or developed from it. As all growth begins and concludes in this substance, it is probably correct to say that here is the seat or foundation of organic life. In the center is a small round body called the nucleus, in which is a still smaller dot termed the nucleolus.
The internal portion of the cell is filled with a fluid, the latex or sap of circulation, in which float a great number of exceedingly minute granules of matter. During the growth of the part, this liquid is in almost constant motion. In many plants this movement of liquid with enclosed granular matter may be readily seen under the microscope. When the cell attains its full growth and has performed its office in connection with active growth, the protoplasm and nucleus disappear, and the cell walls gradually become thickened by the deposition of cellulose and lignin in the interior of the cell. All growth takes place by cell multiplication, by either division or budding. In some cases buds are formed on living cells that gradually assume the form and dimensions of the parent cell when it takes its proper place in the tissue of which it forms a part. But by far the larger part of vegetable growth is the result of cell division. When a cell is about to be divided in the process of natural growth, it first becomes slightly elongated, then a line is drawn through the center of the nucleus at right angles to the longitudinal axis of the cell. This separates the nucleus into two parts, each of which assumes the form, and becomes, in fact, a distinct nucleus.
At the same time the cell wall begins to contract in a line immediately above and corresponding to the line of division through the nucleus; this constriction continues to deepen till the cell is separated into two distinct cells, separated by a wall of cellulose. The rapidity with which cell multiplication takes place in certain cases may be learned from the example of certain fungi in which it is estimated that from three to four hundred millions are formed per hour. As stated above, all growth takes place in the newer cells. In exogenous trees the older cells gradually become closed up by the deposition of a mucilaginous substance known as sclerogen. This contains the coloring matter of wood, and from its accumulation in the cells the older and central portions of the trunks of trees assume a darker color and become more firm and solid. All the growth of such trees takes place in' the cambium cells between the bark and the wood, and the sap circulates principally through the white wood or alburnum. Though the cell is individually so insignificant, yet it is the real basis of all organic structure; and though it is the real seat of all life and growth, yet we may dissect the tissue and analyze the cell itself, and still the directing principle, the building force, escapes us.
The most searching investigation, the most exhaustive analysis gives us no clew to the hidden architect who arranges the atoms into molecules, and these into protoplasmic matter, building up this into cells from which all organic structure is formed. We trace these operations towards the source of power as far as science can guide us, and we reach a boundary beyond which even "intellectual vision" will not carry us. In trying to define the force under whose impulse the organic is built up from the inorganic, we use words, the meaning of which we do not understand, and employ terms the force of which we do not comprehend. Canon City, Col.