OXYGEN RESPIRATION ^^ 



carbon dioxide; 2. Wash bottle with water, or with moist scraps 

 of paper, which serves to moisten the air which was dried by 

 the soda Hme (this is necessary to prevent the drying up of 

 the research material); 3. Container with plant material; 4. 

 Absorption vessel which is either (a) wash bottle of sulphuric 

 acid, (b) potash apparatus, (c) small weighed wash bottle of 

 sulphuric acid, and (d) control bottle of sulphuric acid, or (a) 

 Pettenkoffer tubes and (b) collecting tube; 5. Mercury 

 regulator; 6. Air pump. 



By the methods just described, the respiratory intensity 

 can be measured for various conditions. A control experiment 

 is also made possible by using two or more lots of plant material 

 and two or more series of absorption apparatus simultaneously 

 for each experiment. However, if it is also necessary to measure 

 the absorption of oxygen, wholly different apparatus is required. 

 It must be pointed out at once that a determination of the 

 oxygen absorption without a simultaneous measurement of 

 the quantity of carbon dioxide given out, in the case of experi- 

 ments in plant respiration, may lead to incorrect results since 

 the oxygen is not uncommonly used for incomplete oxidation 

 processes which are not attended by the formation of COo. 

 This assimilation of oxygen, which is often connected with an 

 unimportant release of heat, must not be confused with true 

 respiration. 



From this it is apparent that the determination of the absorp- 

 tion of oxygen must always take place simultaneously with the 

 determination of the liberated CO2 and so serves to measure 



CO" 

 the value of -^ir-"- These determinations are best carried out 

 U2 



by gas analysis. The plant material is inclosed in a suitable 



container with pure air. After the passage of a given interval 



of time,'' samples of gas are removed from the container and 



^' The dynamics of any physiological process are best studied bj' observations 

 of the time required to do a certain amount of work, rather than by measurements 

 of work done in equal times (cf. Osterhout, W. J. V. Science. 48: 172-174. 

 1918). This is an inherent fault in methods which require a titration or a meas- 

 urement of absolute changes in gaseous content. It has been avoided in some 

 of the new methods, notably in the colorimetric methods as used in the Osterhout 

 apparatus described at the end of the section. — Ed. 

 3 



