122 GENERAL BOTANY 



Another striking difference between the oxidations in the living 

 cells of plants and animals and the combustion of coal or 

 wood is found in the temperatures at which the two processes 

 take place. In animals respiration goes on at the normal tem- 

 perature of the animal body, which does not exceed 100 Fahren- 

 heit. The temperatures at which combustions are made possible 

 are known to be much higher than that at which living matter 

 could continue to exist. 



The above comparison of the combustion of coal or wood and 

 respiration in living organisms may be summarized as follows : 



Respiration is like combustion in that oxygen is necessary 

 for both processes and both processes yield energy and carbon 

 dioxide, or energy, carbon dioxide, and water, as final by-products. 

 It also differs from combustion in the complexity not only of 

 the compounds broken down but of the waste products which 

 result from the oxidation processes. 



The function, or use, of respiration is much the same as 

 combustion in an engine, in that it liberates energy which can 

 be used directly or can be transformed so as to furnish power 

 for work of various kinds. In the living cells of seeds, leaves, 

 stems, or roots the energy released by respiration is used for 

 making new protoplasm, for cell division, for protoplasmic 

 streaming, and for other vital processes necessary to the life 

 of the plant organism. 



This energy, as the student will recognize, is different in 

 origin and in function from the external energy absorbed from 

 sunlight by the chlorophyll and used in photosynthesis for the 

 building of sugar and starch. The latter energy enables green 

 plants to make sugar, which forms the basic organic food for all 

 plant and animal life, while the energy released by the respira- 

 tory process is necessary for maintaining the vital processes of all 

 cells, whether they are furnished with green chlorophyll or not. 



The mechanism of plant respiration is very different from that 

 of animals in that the plant is not furnished with lungs and an 

 elaborate blood system for absorbing and distributing oxygen to 

 the living tissues of the plant body. The living cells which 

 we have observed in wood rays and in the wood proper are 



