RESPIRATION BY LEAVES 



165 



s^\ 



Demonstration 13. Place any green water plant in a battery jar 

 partly filled with water, 1 cover the plants with a glass funnel, and 

 invert a test tube full of water over the mouth of the funnel. Place 

 the apparatus in a warm sunny window. Bubbles of gas are seen to 

 rise from the plant. After several hours in the direct sunlight, enough 

 of the gas may be obtained by dis- 

 placement of the water to prove, 

 by the rapid oxidation of a glow- 

 ing splinter of wood in the gas, 

 that oxygen is present. 



That oxygen is given off as a 

 by-product by green plants is a 

 fact of far-reaching importance. 

 The green covering of the earth 

 gives to animals an element 

 that they must have, while the 

 animals in their turn supply 

 to the plants carbon dioxide, 

 a compound used in food mak- 

 ing. Thus a widespread relation 

 of mutual helpfulness exists be- 

 tween plants and animals. 



Respiration by leaves. All living things require oxygen. It 

 is by means of the oxidation of food materials within the plant's 

 body that the energy used in growth and movement is released. 

 k plant takes in air with its oxygen largely through the stomata 

 of the leaves, to a less extent through the lenticels 2 in the stem, and 

 through the roots. Thus rapidly growing tissues receive the 

 oxygen necessary for them to perform their work. One of the 

 products of oxidation in the form of carbon dioxide is also passed 

 off through these same organs. It can be shown by experiment 

 that a plant uses up oxygen in the darkness and gives off carbon 

 dioxide; in the light the amount of oxygen given off as a by- 

 product in the process of carbohydrate-making is much greater 

 than the amount used by the plant in respiration. 



1 Water contains air in solution, including some carbon dioxide, but the amount 

 may be too small. Immediate success with this experiment will be obtained only 

 if the water has been previously charged with carbon dioxide. 



2 Lenticels (lSn'ti-sSls) : lens-shaped spots or warts on the surface of young 

 stems and shoots of peach, apple, and other trees. 



H. BIO — 12 



."v/ater-aud 



car-bon 

 diovicCe, 



green plant. 



Explain just what is happening here and the 

 conditions necessary to bring it about. 



