LOSS OF OXYGEN IN RESPIRATION 



133 



trol was found free from C0 2 , thus proving the absence 

 of any accidental contamination during the period of the 

 experiment. The process was repeated at temperatures 

 of 18°, 22 , 27 and 32 C. The estimation of the C0 2 

 evolved in the bottle containing the plants gave the following 

 results. 



Table XVIII. — Rate of Respiration at Different 

 Temperatures 



The rate of loss by respiration at any intermediate 

 temperature can be found from the curve plotted on these 

 data. Since the average rate of evolution of oxygen under 

 moderate intensity of light at 18 C. is about 150 c.mm. per 

 hour, the loss of oxygen in respiration is about 4-4 per cent. 



I have also determined the percentage of respiratory 

 loss by another method. It will be shown in Chapter 

 XXIII. that the production of carbohydrate during photo- 

 synthesis causes an increase of weight. In a typical experi- 

 ment this increase in the weight of the plant after 9 hours' 

 exposure to diffuse light from the sky was 1-4 mg., or 

 0-155 mg. per hour. After this preliminary experiment, 

 the plant suspended from the balance in the dark lost 

 through respiration o-i grm. in weight after 14 hours, or 

 0-0071 grm. per hour, at 18° C. average temperature. The 

 percentage of loss is therefore : 



0-0071 X 100 



4-6 



o-i55 



In the absolute determination of photosynthesis, the 

 volume of oxygen is reduced to N.T.P., and a correction 

 added for respiration at the particular temperature. 



