SECTION II. CELL STRUCTURE AND 

 ANATOMY 



CHAPTER III 



THE CELLULAR STRUCTURE OF PLANTS 



The bodies of all plants and animals have been found to be 

 composed of organic units termed cells. Each cell unit in its 

 simplest form is a boxlike structure with bounding cell walls 

 inclosing the cell cavity in which is lodged the living substance 

 of the organism. These structural units of the plant and animal 

 body were first called cells on account of their fancied resemblance 

 to the cells of a honeycomb or of a prison. 



The lowest forms of plants and animals are unicellular in 

 structure, but the higher forms are multicellular, consisting of 

 innumerable cells of the most varied form and function. Thus 

 muscles and bones, roots, stems, and leaves, are all built up of 

 cells, which are adapted in their form and structure to the 

 peculiar functions of each particular organ or part. 



Just as bricks or stones are used as structural units with 

 which to build a wall or a tower, so we may conceive of the 

 bodies of the higher animals and plants as being built up of liv- 

 ing cell units. It has been found also that nearly all organisms 

 have their origin in a single cell, the fertilized egg cell. 



In the building of the complex organism from this single egg 

 cell the egg first divides into a multitude of simple cells like 

 itself, and these similar cells are then gradually transformed into 

 the different kinds of cells which make up the various tissues 

 and organs of the adult body. 



This conception that all living organisms, however diverse in 

 their character, are composed of similar structural cell units and 

 of a common living substance, protoplasm, is now known as the 



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