Protoplasm
(from proton, first, and plasma, formed matter). A word frequently used by students of the microscopic structure of plants and of animals. The term was first proposed, in 1846, by the distinguished German botanist, Hugo von Mohl, and is still used in the sense employed by him, to denote the transparent, soft, semi-fluid, jelly-like substance found in young, living cells of all plants. He was the first to appreciate the true importance of this substance. Before his observations were made, it had been very generally believed that the wall which bounds each cell, and remains very evident after the cell contents have been emptied out, was the essential part of the cell; and the name "cell" was given to the space inclosed by the cell wall. It seems to have been first used, in 1665, by the English microscopist, Robert Hooke, who says: "Our microscope informs us that the substance of cork is altogether filled with air, and that that air is perfectly inclosed in little boxes or cells, distinct from one another." Von Mohl recognised that the really essential part of the cell is the Protoplasm; and that by it other cell contents and the cell wall are produced. This view has been fully confirmed by later investigations, and also by the fact that among Ferns, Mosses, and other flowerless plants, the essential reproductive cells, for a time, consist of Protoplasm alone, without a cell wall.
In young, growing tissues, such as the tip of the root of a Bean, or of any other large seedling, the Protoplasm at first frequently fills the space bounded by the cell wall. At one place lies a denser, round or oval mass, also composed of Protoplasm, called the "nucleus," with a clearly-defined edge. As the cell grows larger, the Protoplasm does not increase so much as to fill the space within the cell wall. Cavities appear in it, occupied by fluid or cell sap. These are, at first, separated by plates of Protoplasm; but, with continued increase in size of the cell, the vacuoles unite, and form one large cavity in the centre, occupied by cell sap; and the Protoplasm forms only a layer lining the cell wall.
When a living cell is laid in strong glycerine or in alcohol, the water of the cell sap and of the Protoplasm is drawn out of the cell by these fluids, and the contents shrink away from the cell wall, leaving an empty space between them and the wall all round. The outer surface of the shrunken mass is clearer and less granular than the rest, and looks almost like a distinct coat. It was formerly known as the "primordial utricle," but is now more usually called "ectoplasm" (from ektos, outside, and plasma). The inner substance, called "endoplasm" (from endon, inside, and plasma), is more granular, and incloses starch grains and other bodies connected with the nourishment of the tissues of the plants.
Living Protoplasm is constantly undergoing rapid changes of composition, taking into it new food, forming new bodies or products, and getting rid of materials that have done their work, and must be thrown out. All this implies constant changes in the position of the minute particles of which Protoplasm consists, though these movements are too slow, and the particles are usually too small, to permit of their being followed under the microscope. But in many cells (probably in most) the Protoplasm is seen to be moving round and round the cell, if it forms only a layer lining the cell wall; or it may be seen to move along the slender plates between the vacuoles, from the outer layer inwards towards the layer around the nucleus, and again outwards. Often a thin thread or plate shows two streams on its sides moving in reverse directions. Cells that consist of Protoplasm without a cell wall, are usually able to move freely about in water by moving fine threads or cilia, or by pushing out pseudopodia, or outgrowths, from the surface, and flowing towards these, e.g., in some stages of Myxomycetes, such as Flowers of Tan, and other Fungi closely related to it.
The chemical composition of Protoplasm is very complex. It belongs to the group of substances similar in nature to white of egg, or albumen. It is very similar in its properties in plants and in animals, in which latter it has been called "sarcode" (from sarx, flesh). When laid in a solution of iodine, it becomes yellowish or pale yellowish-brown. Dyes, such as magenta, eosin, and other aniline colours, carmine, logwood, &c., very generally colour dead Protoplasm readily, especially the nucleus; but the living substance resists their action. A dilute solution of caustic potash dissolves Protoplasm, and is therefore often used, in microscopical work, to clear it out of sections where the chief desire of the operator is to see the arrangement of the cell walls only. Other tests for distinguishing Protoplasm are also occasionally used; but for these, inquirers are referred to such works as Sachs' "Textbook of Botany," Henfrey's "Elementary Course of Botany," Bower and Vine's "Practical Botany," or other works dealing technically with the subject.