. Essentials of biology presented in problems. Biology. COMPOSITION OF LIVING THINGS 29 an onion shows well, as do thin sections of a young stem, as the bean or pea. I have found one of the best places to study a tissue and the cells of which it is composed in the leaf of a green water plant, Elodea. In this plant the cells are large, and not only the outline of the cells, but the move- ment of the living matter -nithin the cells, may easily be seen, and most of the parts described in the next paragraph can be demonstrated. Cells. —JAceU may be defined as a tiny mass of living matter, either l
. Essentials of biology presented in problems. Biology. COMPOSITION OF LIVING THINGS 29 an onion shows well, as do thin sections of a young stem, as the bean or pea. I have found one of the best places to study a tissue and the cells of which it is composed in the leaf of a green water plant, Elodea. In this plant the cells are large, and not only the outline of the cells, but the move- ment of the living matter -nithin the cells, may easily be seen, and most of the parts described in the next paragraph can be demonstrated. Cells. —JAceU may be defined as a tiny mass of living matter, either living alone or forming the building material of a living thingf The living matter of which all cells are formed is known as protoplasm (from two Greek works meaning first form). When viewed under a high magnification of a compound microscope, it is a grayish, semi- fluid mass, seemingly almost devoid of any structure. A careful observer will find, however, that the material seems to be made of a ground mass of fluid \dth innumerable granules of various size and form float- ing in the fluid portion. All plant and animal cells appear to be alike in the fact that every living cell possesses a structure known as the nucleus (pi. nuclei), which is found within the body of the cell. jjl ,The nucleus is composed of h'\Tng matter like the rest of the cell, although it seems to differ in some chemical way from that part of the cell sur- rounding it. This is seen when a plant or animal is placed in a liquid containing some dye such as logwood. Certain bodies in the nucleus take up the stain much more readily than the rest of the living matter of the cell, taking on a deep black color, called the chromosomes (color-bearing tiodicsj. The chromosomes, which arc lielieved to be always definite in number for every tissue cell, are of much interest to scientists. It is found that each. Diagram of a cell (after Wilson). The cell protoplasm contains spaces to hold liquid cell sap (); just
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