522 



RESPIRATION 



The quantity of respiratory enzymes present in the protoplasm undoubtedly is 

 also a factor which affects the rate of respiration. 



2. Temperature. — As is true of most other biological processes temper j;ture 

 effects upon the rate of respiration are rather complex. In general, within 

 certain limits, increase in temperature results in an increase in the respiration 

 rate. As in photosynthesis and in enzymatic reactions a definite time factor 

 effect is often evident. The general principles regarding the effect of tem- 

 perature upon respiration rates are illustrated by the data shown graphically 

 in Fig. 114. In this experiment pea seedlings were used as the experimental 



3 4 5 



TIME IN HOURS 



Fig. 114. Relation between time, temperature, and rate of respiration of pea seed- 

 lings. Dotted lines represent period during which temperature of seedlings was 

 changed from 25° C. to indicated temperatures. Data of Fernandes (1923). 



material. In the temperature range between 0° C. and 45° C. increase m 

 temperature resulted in an increase in the initial rate of respiration. At tem- 

 peratures above approximately 30° C. the rate of respiration showed a de- 

 crease with time, which became more marked the higher the temperature. 



For the pea seedlings used in this experiment the optimum temperature 

 would appear to be about 30° C, as this is approximately the maximum 

 temperature at which there is a maintained rate of respiration. The optimum 

 temperature for respiration, considered in this sense, is not the same for all 

 plant tissues. For some it is clearly higher than the value obtained in this 

 experiment with pea seedlings and for others it is lower. 



The exact nature of the "time factor" which becomes increasingly effective 



