38 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



supply in the rest of the plant. This undoubtedly accounts for the 

 fact that the plant is able to continue its initial respiratory rate for 

 so long a time, which is in decided contradistinction to the behavior 

 of the excised leaves when these are not suppHed with carbohydrates. 



In table 10 are given the results of the rate of carbon-dioxid emis- 

 sion from sunflower leaves which had been cut from the plant. 

 The petioles of the leaves were immersed in a sterilized nutrient 

 solution which contained only inorganic salts. The following analyti- 

 cal data give an idea of the changes of material in the leaves during 

 the period of respiration. 



Figure 8. 

 Solid line represents rate of 

 respiration of 8 leaves of Heli- 

 anthus annuua at 24°; petioles 

 in a nutrient solution contain- 

 ing no organic substances. 

 Values taken from table 10. 

 Broken line represents rate of 

 respiration of 15 leaves of Can- 

 ada Wonder bean; petioles in 

 nutrient solution containing no 

 organic substance. Values tak- 

 en from table 11. The ordinate 

 gives mg. CO2 per hour per 

 gram dry material, the abscissa 

 the time in hours. 



In table 11 similar results are given for excised bean leaves. 

 From the curves of these respiratory rates, given in figure 8, it is 

 evident that in the excised leaves the rate of CO2 emission declines 

 rapidly when the only supply of carbohydrates is the material stored 

 in the leaf, and that these respiratory rates decrease with but a slight 

 variation, except at about the forty-eighth hour. These graphs 

 represent the normal course of respiratory activity of excised leaves. 



