CHAPTER VII 
CELLS AND TISSUES 
Structure and Function of Cells 
Position of the Cell in Plant Life. — Before proceeding to the 
study of the adult stage of the plant more must be known about 
the cell. If with a sharp razor a very thin section from any part 
of a plant is made and observed with a microscope, it will appear 
to be divided into many small divisions. <A section through the 
growing portion of a root looks like Figure 105. These little 
divisions with what they 
a i ee soe ee contain are the cells. Cells 
Op ce ae vary much in shape and are 
san i ane} a a so small that usually four or 
is = five hundred of them could 
be laid side by side ona line 
not more than an inch in 
length. They are rarely more 
than yi, of an inch, and 
sometimes less than yoy55 of 
an inch in diameter. Al- 
Perret! though cells are so exceed- 
Fic. 105.— A small portion of a length- ingly small, nevertheless, it 
wise section through the growing region is within them that all life 
of a root showing the cells. Very much processes take place. For 
enleneed this reason cells are often 
defined as the units of all plant and animal life. Plants need 
phosphate, nitrates, etc., because the cells must have them. All 
the problems of the plant relating to the soil, light, temperature, 
etc., are problems of the cell. The plant is made up of a countless 
number of cells and the activities of the plant are simply the sum 
of the activities of the many cells of which the plant is composed. 
Discovery of the Cell and Its Structures. — That plants and 
animals are composed of cells was not revealed until the inven- 
tion of the microscope, which, although very rude in its con- 
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