The Controlling Influence of Carbon Dioxide. 



155 



of Ohrwall, Beneclicenti and Treves, Straub, Lovatt Evans, Starling and 

 Jerusalem, and Starling and Kaya in muscular tissue. 



Section VIII. — Conclusions. 



The results obtained may now be summarised. That this may be done 

 more effectively it will be well to recall briefly the main results obtained in 

 Parts I and II of these researches, which were as follows : — 



1. The resting stage of the moist seed is primarily a phase of narcosis 

 induced by the action of carbon dioxide. 



2. Both the arrested development in the case of the moist maturing seed 

 and the widely occurring phenomenon of delayed germination in the case of 

 the moist resting seed, are related to an inhibitory partial pressure of carbon 

 dioxide in the tissues of the embryo. 



3. Germination is related to a lowering of this inhibitory partial pressure 

 of carbon dioxide in the tissues. 



4. The inhibitory value of a given carbon dioxide pressure diminishes with 

 a rise of temperature. 



5. The inhibitory value of a given carbon dioxide pressure diminishes with 

 a rise of oxygen pressure. 



In Part III the investigation has been extended to plant tissues in 

 general, in order to determine the mechanism of this narcosis. The 

 influence of carbon dioxide upon respiration has been first studied, in view 

 of the fact that respiration appears closely connected with growth by cell 

 division. The conclusions reached may be summarised as follows : — 



1. The rate of anaerobic C0 2 production in plant tissues is depressed by 

 carbon dioxide. 



2. This depression of C0 2 production is not due to permanent disorganisa- 

 tion. It passes away as soon as the depressant concentration of CO2 is 

 removed. 



3. Quantitatively the degree of depression at the temperatures used 

 appears to be proportional to the square root of the concentration of C0 2 , 

 over a range from to 50 per cent. C0 2 at one atmosphere pressure. Above 

 50 per cent, the effect of increasing the concentrations becomes gradually 

 less marked. 



4. This depressant action of carbon dioxide is not limited to anaerobic 

 C0 2 production, but occurs also in aerobic respiration in the presence of 

 oxygen. 



5. The depression of aerobic respiration under carbon dioxide is shown 

 when measured either by 2 consumption or C0 2 production. 



