PLANT LIFE, 



PART I: THE PLANT BODY. 



INTRODUCTION. 



1. Units of structure. — An examination of any plant by- 

 proper methods reveals the fact that it is made up of one or 

 more units of structure. The unit of structure of a brick 

 wall is the individual brick. Each has a definite shape and 

 relation to others, upon which the form of the wall depends. 

 The unit of structure of a plant is called a cell. The cells 

 have each a definite form and relation to others, and upon 

 these two factors the form of the entire plant depends. 



But between the plant and the brick wall there is this im- 

 portant difference. The bricks, after being perfectly formed, 

 were put together. The cells of the plant are produced where 

 they lie and gradually grow to a mature form and size. The 

 bricks are originally disconnected ; the plant-cells are con- 

 nected by origin, and only as they become mature do they 

 separate, if at all. 



2. The cell. — A plant-cell is a minute portion of living 

 matter, called protoplasm or plasma, generally surrounded by 

 a membrane, called the cell-wall (fig. i). If the brick in 

 the previous illustration be taken to represent the protoplasm, 

 the mortar may be considered as the cell-wall.* 



* This illustration must be carried no further than to show the relation 

 of position of these two parts of a cell. 



