76 EXPERIMENTAL PLANT PHYSIOLOGY 



place carbon-dioxide continues to be evolved, thus 

 there ceases to be any relation between the amount 

 of oxygen taken in and that of carbon-dioxide given 

 out. 



The change in the level of the liquid which was 

 observed in the above experiment, after the apparatus 

 had been set up for some time, was largely due to 

 the fact that intramolecular respiration had begun. 

 Another factor which caused movement of the column 

 of liquid was the evaporation of water-vapour from 

 the surface of the peas and paper.) 



Experiment 46 



Aim. — To determine the amount of carbon-dioxide 

 that is given out in the process of respiration. 



Method. — From Experiment 45 it is seen that, 

 within very rough limits, the amount of carbon-dioxide 

 expired is equal to the amount of oxygen inspired. 



Assuming, then, that these amounts are equal, the 

 quantity of oxygen measured in Experiment 44 may 

 be taken also as a measure of the amount of carbon- 

 dioxide expired. 



Experiment 47 



Aim. — To find out whether a plant breathes in the 

 dark as well as in the light. 



Method. — The foregomg experiments can be worked 

 again, the apparatus being kept in the dark. 



Observations. — Similar observations wiU be obtained. 



Inference. — Plants breathe always, night and day. 



Experiment 48 



Aim. — To find out whether a plant can live if it is 

 deprived of oxygen. 



Method. — In this experiment some substance must 

 be used that has the power of absorbing oxygen from 

 the air. Pyrogallic acid answers this purpose. In 



