THE CELL 



15 



Englishman, Robert Hooke, while examining objects in general 

 with his new and primitive microscope, chanced upon a piece of 

 cork. He saw a myriad of tiny cavities, empty, with heavy 

 walls (Fig. 6). He described them as "httle boxes or cells 

 distinct from one another" (Fig. 7). Thus were discovered the 

 dead and empty chambers which are the skeleton of the plant. 

 The li^'ing matter within them was not seen and understood until 

 nearly two centuries later. 



The study of cells constitutes that branch of science known as 

 cytology. 



Fig. 8. — Drawing of a group of plant cells from an onion with the contents 

 plasmolyzed (a fine glass needle is shown penetrating the walls of cellulose). 



The Shapes of Cells. — Plant cells are usually angular in shape, 

 their form being maintained by the heavy cellulose wall. The 

 absence of such a wall permits animal cells to assume a globular 

 form or at least a smooth contour. Plant cells are sometimes 

 shaped like rectangular boxes (Fig. 8), but more commonly 

 they are irregular 12- or 14-sided polyhedrons (Fig. 9). Work 

 done on the shapes of plant cells by Frederick T. Lewis leads to 

 the conclusion that the orthic tetrakaidecahedron, a 14-sided 

 figure with eight hexagonal facets and six quadrilateral ones, 

 is the most common form among plant cells. There are other 

 unique shapes assumed by highly specialized cells, to be described 

 later. 



The Parts of Cells. — The hollow cells of seasoned lumber or 

 cork constitute the nonliving cellulose skeleton of the plant. 

 It is the contents of these skeletal cavities which give the property 



