496 Our Surroundings 



have passed through the membrane into the molasses which is a 

 thicker solution. 



If preferable, an egg may be used to illustrate osmosis. Fasten 

 one end of a small open glass tube, 8 to 12 inches in length, to 

 the small end of the egg, by allowing melted wax to harden around 

 the place where the end of the tube touches the shell. Then, 

 after passing a hat pin or wire through the tube, puncture the 

 shell and the membrane of the small end of the egg. Remove 

 the shell from the lining membrane at the larger end of the egg 

 over an area of about ^ of an inch in diameter. Place the egg in 

 a small tumbler of water with the exposed membrane in the water. 

 After two hours examine and observe what has happened. 



Experiment to Show the Upward Course of Soil Water in a 

 Root. Place a growing plant, a carrot for example, in a vessel 

 containing red ink, in such a way that the lower part of the root 

 dips into the fluid. Leave the plant until a red color shows in 

 the leaves, indicating that the fluid has been absorbed by osmosis 

 through the membranes of the root hairs. 



Digestion. Before a green plant can use the food which it 

 has made to build new cells and to supply energy, it must first 

 digest the food. This is accomplished largely in the leaves by a 

 special substance called diastase, an enzyme which changes starch 

 to soluble sugar. 



Circulation and Assimilation. Digested food flows in solu- 

 tion through the veins in the plant and is taken up by the cells 

 throughout the plant by the process of osmosis. The movement 

 of this liquid may be compared to blood circulation, as it is a 

 movement of liquid conveying food material in the plant body 

 to its various parts. As it passes into the cells, the digested food 

 is assimilated, that is, it is made a part of the growing plant and 

 is used to build new cells. 



Excretion. Plants excrete water vapor, oxygen, and carbon 

 dioxide. The leaves give off water vapor much as the human skin 

 gives off perspiration. They also give off oxygen. Both leaves 

 and stems excrete carbon dioxide in respiration. 



Reproduction. Plants, as well as animals, reproduce their 

 kind. Reproduction is carried on through flowers or blossoms. 



