186 



FIRST YE.AE SCIENCE 



The plant root takes up its water in the same way the 

 water was taken into the sugar solution of the potato cup 

 or of the carrot. The water or sap within the substance 

 of the root is denser than the soil water, just as the sugar 

 solution was denser than the water outside. It has been 

 found that whenever two liquids or gases are separated 

 by an animal or plant membrane, there is an interchange 

 of the liquids or gases, the less dense liquid or gas passing 

 through more rapidly. This is called osmosis and is of 

 the greatest importance to both plants and animals. 



All animals and plants are made up of exceedingly 

 minute parts, called cells. Fig. 84 shows the cells in a leaf 



and the leaf hairs greatly 

 magnified. The higher 

 plants and animals are 

 composed of vast num- 

 bers of these cells. The 

 cell usually has a thin 

 cell wall, which in living 

 and growing cells in- 

 closes a colorless semi- 

 fluid substance called 

 protoplasm. This pro- 

 Fig. 84. toplasm is the living part 

 of the plant. It is found 



in all the cells where growth is taking place, where plant 

 substances are being made, or where energy is being trans- 

 formed. It has the power of dividing and forming new 

 cells, and it is in this way that the plants grow. 



The little root hairs are one kind of plant cells. They 

 consist of a thin cell wall within which is protoplasm and 

 cell sap, a solution of different plant foods. Since the pro- 

 toplasm and cell sap are denser than the soil water, more 

 liquid moves into the cell than from it. A little of the 



