CHAPTER VII 



THE HISTOLOGY OF THE CELL 



The Cell. All parts of plants agree in being built up or 

 microscopic elements which have received the name of cells (p. 65). 

 The cells which are present in a woody plant, such as the Oak, 

 may be living or dead. ^Head-cells perform an important func- 

 tion in giving firmness and .rigidity to the plant. They may 

 also conduct water from the roots to the leaves, and protect the 

 deeper parts of the plant from injury. Cells may be separate, 

 as in the ripe pulp of the Tomato, but in most cases they are 

 united to form a tissue. Cells vary very much in form and 

 development, and upon this will depend the kinds of tissue 

 which they may produce. It will be an advantage to begin by 

 studying the individual cell. 



The Structure of a Cell. As living cells change with 

 age it will be better to take a young cell and to follow it until it 



becomes mature. 

 P In a young cell, 



such as can be seen 

 in the cortical (p. 

 66) tissue of the 

 stem of most 

 plants, the follow- 

 ing three principal 

 constituents can be 

 distinguished. On 

 the outside a mem- 

 brane separates the cell from others which surround it, and 

 is called a cell- wall. In close contact with the whole surface 

 of the cell-wall, and filling the entire cavity of the cell, is the 

 protoplasm. Embedded in the protoplasm is a . denser 

 granular portion which is called the nucleus. 



cw 



FIG. 101. The left-hand. figure, a young parenchyma 

 cell; the right-hand figure, an older cell. CW, 

 cell-wall ; P, Protoplasm ; N , nucleus ; N L, 

 nucleolus ; V, vacuoles. 



