140 



Mr. F. Kidd. 



dioxide present which must be considered as the effective value in producing 

 the observed retardation of respiration in any case. In our experiments, 

 however, in view of the fact that the changes in total pressure are relatively 

 small, we have taken the percentage figure for carbon dioxide as expressing 

 its effective value. A correction for this error would slightly steepen our 

 curves. 



It must be further pointed out that it is the tissue-pressure of C0 2 

 which is ultimately effective. The tissue-pressure will be higher than 

 the external pressure of C0 2 , according to the rate of CO2 production in the 

 tissues. The data obtained are sufficient to correct for this. As it seemed 

 doubtful whether sufficient accuracy in observation had been obtained to 

 make this correction worth while, it has not been made. The result of such 

 a correction would be again to slightly steepen our curves. 



The results are given throughout in cubic centimetres of gas at 0° C. and 

 760 mm. pressure of mercury. 



Section III. — The Influence of Carbon Dioxide upon Anaerobic Respiration 



in Seeds. 



In the following experiments living seeds in germinating conditions and 

 also maturing seeds were used as material, the effect upon anaerobic respiration 

 (that is to say, C0 2 production in tissues in the absence of oxygen) of increased 

 concentrations of C0 2 in an atmosphere was determined. 



Table I.— Showing the Eetarding Influence of Increased Concentrations of 

 Carbon Dioxide upon the Kate of Anaerobic Respiration in Peas 

 (without Testas), otherwise in Germinating Conditions save for the 

 Absence of Oxygen. 



Initial C0 2 in 



atmosphere 

 of N 2 and C0 2 . 



Total anaerobic C0 2 production. 



Final 



co 2 



in atmo- 

 spheres. 



After 22 hours. 



After 50 hours. 



After 72 hours. 



After 146 hours. 



per cent. 



c.c. 



c.c. 



c.c. 



c.c. 



per cent. 







16 



33 



58 



171 



14 



28 



9 



27 



41 



111 



35 



48 



3 



8 



13 



45 



50 



Conducted in dim diffuse light. Early Sunrise peas, without testas, set dry on wet sand, 

 45 c.c. sand, 21 c.c. tap water, 10 peas in each experiment. 

 C0 2 production estimated from analysis. 

 Temperature, 20 '5° C. thermostat. 



In the foregoing Table (I) of results it will be at once seen that increased 

 concentrations of C0 2 have a marked effect in decreasing the anaerobic 



