PLANT ROOTS 



371 



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. Figure 110 shows the cells in a leaf and the 

 leaf hairs greatly magnified. The higher plants and animals 

 are composed of vast numbers of these cells. The cell 

 usually has a thin cell 

 wall, which in living and 

 growing cells incloses a 

 colorless semi-fluid sub- 

 stance called protoplasm. 

 This protoplasm is the 

 living part of the plant. 

 It is found in all the cells 

 where growth is taking 

 place, where plant sub- 

 stances are being made, 

 or where energy is being 

 transformed. 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 

 cell solution does move out, however, and it is this which 

 helps to dissolve the soil particles. The protoplasm in the 

 cell regulates to some extent the interchange of liquids. 



Experiment 113. Cut off the stem of a thrifty geranium, be- 

 gonia, or other plant an inch or two above the soil. Join the plant 



FIGURE 110 



