250 TEXTBOOK OF PLANT PHYSIOLOGY 



the various endothermic reactions connected with synthetic proc- 

 esses, the plant requires energy, just as do engines. This energy 

 is secured through the combustion of carbohydrates. It differs, 

 however, from the burning of fuel in a furnace, since in protoplasm 

 the energy of oxidation passes into other forms of chemical energy 

 and is emitted as heat energy only after having been utilized and 

 changed. These internal transformations of energy which accom- 

 pany respiration are, however, very little understood; hence, the 

 total quantity of energy obtained through respiration is still 

 measured by its thermal effect. 



Respiration has always been considered as being closely con- 

 nected with life. This is but natural, since life is subject to a 

 continuous liberation of energy obtained through respiration. 

 Therefore, the investigation of the respiratory process is one of the 

 central problems of general physiology. And the deepest analysis 

 and furthest penetration into the chemical and dynamic nature of 

 this phenomenon promises us a clearer understanding of the com- 

 plex processes called life. 



In both animal and plant organisms, respiration is essentially 

 of the same nature. It consists in obtaining energy for the cells 

 during the combustion of carbohydrates. Usually, the animal 

 organism consists of a massive body to some parts of which gaseous 

 oxygen cannot easily penetrate ; hence, in order to provide all cells 

 with oxygen a special complex mechanism is required, which con- 

 sists of a blood-circulating system with its conveyors of bound 

 oxygen, the red blood corpuscles, and respiratory organs, where the 

 blood can be saturated with oxygen and freed from the accumu- 

 lated carbon dioxide. The complexity of these essential, yet ad- 

 ventitious, organs has obscured the true nature of respiration. 

 Even as late as the beginning of the nineteenth century, the opin- 

 ion still prevailed that respiratory movements and blood circula- 

 tion were the main features of respiration, and, consequently, the 

 existence of respiration in plants was denied. Much effort was 

 necessary to introduce into science the truth that respiration 

 proceeds neither in the lungs nor in the blood, but in each 

 living cell. 



The external conditions of respiration are very much simpler 

 in plants than in animals. Owing to the development of a com- 

 paratively large surface, as a result of gaseous nutrition, the oxygen 

 of the air comes in direct contact with each cell of the plant body. 



