CELL STRUCTURE 



27 



bodies of higher animals or plants and gave to it the name of 

 Sarcode. It was not until 1863 that protoplasm and sarcode 

 were shown, by Max Schultze, to be the same type of substance. 

 Ii the meantime the cell theory of Schleiden and Schwann was 

 made a basis for research on the finer structure of animals and 

 plants and the theory was confirmed for 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), 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 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 

 st anding of a theory, but is one of the fundamental and firmly 

 established facts of biology. 



All cells have the same general structure; all are composed of 



