. Biology . announced theirbelief that all plants and all animals are composed of minuteunits of structure to which, following Hooke, they gave thename cells. But even they did not have the idea of cells that wehave today but regarded the walls as the vital parts. Proto-plasm, as the fundamental living substance, was practicallyunknown, although in 1835 a French naturalist Felix Dujardinstudied the structure of certain foraminifera or naked bitsof Kving matter without cell walls and published his conclusion 26 CELL STRUCTURE 27 that this Hving substance, which he called sarcode, is asimpler fo
. Biology . announced theirbelief that all plants and all animals are composed of minuteunits of structure to which, following Hooke, they gave thename cells. But even they did not have the idea of cells that wehave today but regarded the walls as the vital parts. Proto-plasm, as the fundamental living substance, was practicallyunknown, although in 1835 a French naturalist Felix Dujardinstudied the structure of certain foraminifera or naked bitsof Kving matter without cell walls and published his conclusion 26 CELL STRUCTURE 27 that this Hving substance, which he called sarcode, is asimpler form of Hving matter than that which composes thebodies of higher animals or plants. It was not until 1863 thatprotoplasm and sarcode were shown, by Max Schultze, to bethe same type of substance. In the meantime research on thefiner structure of different animals and plants extended thecell theory of Schleiden and Schwann to form after form, whilethe older view that the walls are the essential parts was gradu-. FiG. 12.—General view of cells composing the growing root-tip of an onion;some cells in stages of division (mitosis, see p. 209). a, Non-dividing cells; b,early stages of nuclear change; c, cells in full mitosis. (From E. B. Wilson.) ally replaced by the modern conception of protoplasm and ceilstructure. It thus follows that the term cell, meaning originally anempty box, then a framework with fluid contents, has come to-mean finally a small unit mass of living material, while the cellu-lar structure of all Hving things has no longer the uncertainstanding of a theory, but is one of the fundamental and firmlyestablished facts of biology. 28 PROTOPLASM AND THE CELL All cells have the same general structure; all are composed ofprotoplasm, of which a part, called the nucleus, is different fromthe remainder of the cell body, or cytoplasm. In the highertypes of living things, where innumerable cells make up thebody of the individual, the cells are specialized to performdifferen
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