316 GENERAL SCIENCE 



Protoplasm has the power to move by contraction. 

 Plants move and change the position of their leaves, while 

 the muscular action is a well-known power. Protoplasm 

 also has the power of taking up materials that it can use 

 as food and rejecting those materials which it cannot use. 

 Protoplasm breathes oxygen, eliminates wastes, and has 

 the power to reproduce its kind of plant or animal 

 (Figure 270). 



The Living Plant. Plants are fed by the elements 

 that they take from the soil and air. From these elements 



they build all the various com- 

 plicated plant structures known 

 as flowers, seeds, roots, and 

 stems. Each part of the plant 

 has its own particular purpose 

 and is correspondingly built. If 

 the plant is properly fed it will 

 FIG. 27i. A sick and a Well develop evenly, but if the soil is 



lacking in some of the essential 



plant foods the plant which grows on it will be weak 

 (Figure 271). 



Cells. A cell is the smallest bit of living matter that 

 can exist alone. All plants and animals are composed of 

 cells which are separate masses of protoplasm, each hav- 

 ing a nucleus and each surrounded by an envelope called 

 the cell wall. Cells vary greatly in size. Some of them 

 may be seen readily with the unaided eye, while others 

 have a diameter of not more than 1/25000 of an inch. 

 In shape they vary from long strings, such as are found 

 in the cotton fiber, to the spherical eggs of animals. 



Tissues. Collections of similar cells, grouped to pro- 

 duce some particular part of a plant or animal, are 

 tissues. Examples of tissues are woody tissue, pith 



