CELL STRUCTURE 



27 



that this living substance, which he called 'sarcode," is a 

 simpler form of living matter than that which composes the 

 bodies of higher animals or plants. It was not until 1863 that 

 protoplasm and sarcode were shown, by Max Schultze, to be 

 the same type of substance. In the meantime research on the 

 finer structure of different animals and plants extended the 

 cell theory of Schleiden and Schwann to form after form, while 

 the 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). 0, 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 cell 

 structure. 



It thus follows that the term cell, meaning originally an 

 empty 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 living things has no longer the uncertain 

 standing of a theory, but is one of the fundamental and firmly 

 established facts of biology. 



