118 VEGETABLE PHYSIOLOGY 



CHAPTER VIII 



RESPIRATION 



OF the gaseous interchanges which were mentioned in the 

 last chapter as characteristic of living protoplasts, the 

 most widespread is that which is marked by the absorp- 

 tion of oxygen. With the exception of a few of the lowlier 

 organisms, all of which are members of the group of 

 Fungi, every living protoplast must be constantly absorb- 

 ing this gas in order not only that its vital activities may 

 continue to be discharged, but that its life itself may be 

 maintained. Withdrawal of oxygen from the environment 

 of the protoplast is after a longer or shorter interval 

 followed by its death. It is true that under certain con- 

 ditions which we shall discuss in a subsequent chapter the 

 interval may be prolonged, but death ultimately ensues. 



This absorption of oxygen is in most cases associated 

 with an exhalation of carbon dioxide, which is generally 

 given off in a volume approximately equal to that of the 

 oxygen taken in. 



The universality of this process is not always easy to 

 demonstrate. It can be ascertained without difficulty in 

 the case of almost all animal organisms, and of such of 

 the vegetable ones as possess no chlorophyll. In the case 

 of those plants which are green, however, there is, as we 

 have already mentioned, and as we shall discuss more fully 

 later, a converse gaseous interchange occurring so long as 

 the green parts are exposed to sunlight, carbon dioxide 

 being absorbed and decomposed, and an equal amount of 

 oxygen being exhaled. This interchange is usually more 

 vigorous than the first one, and the latter is therefore diffi- 



