22 NATURE OF RESPIRATION 



added power to build up the complex food compounds from 

 crude material. By the decomposition of these foods it gains 

 energy to grow and carry on its other vital functions. The work 

 of respiration is carried on more economically by green plants 

 than by animals since in the animal the CO2 escapes in the breath 

 as a waste product, while the plant uses this CO2 during the 

 day time for the construction of foods. Consequently the escape 

 of CO2 can only be observed during the night and cannot be 

 detected in the light unless an examination of very rapidly grow- 

 ing organs be made. If a jar be nearly filled with opening buds 

 of dandelions or rapidly growing shoots and then closed air tight, 

 sufficient COo will be respired in a few hours to extinguish a light 

 that is lowered into the jar. In such instances as these very 

 rapid respiration is necessary to furnish the required energy for 

 growth and the volumes of CO2 expired exceeds many times the 

 volume of CO2 utilized in photosynthesis. A handful of ger- 

 minating peas or beans placed in a closed jar for a few hours better 

 illustrates the giving off of CO2 because here there is no green 

 tissue to absorb any of the CO2. Plants are often considered 

 unhealthful in sleeping rooms at night because of their exhalation 

 of CO2. It is well to remember that the amount of CO2 expired 

 by a plant is small and that a gas jet would furnish more CO2 to 

 the air than a window full of plants. 



We are now in a position to understand the importance of 

 photosynthesis and respiration. Photosynthesis keeps the air 

 pure for breathing, decomposes the simple inorganic compounds 

 and recombines them into foods which represent a certain amount 

 of stored-up energy. Respiration breaks down the foods into 

 products which form the tissues of the plant and sets free the 

 energy necessary for the accomplishment of its growth and move- 

 ments. In the animal and plant the oxygen decomposes the foods 

 rather slowly and the energy set free is principally manifested as 

 heat and as the power that enables them to perform their various 

 activities. If the decomposition is sufficiently rapid light as well 

 as heat appears. This is the nature of the reaction when plant 

 tissues, such as wood, are burned. The oxygen so rapidly de- 

 composes the products which compose the wood that heat and 



