RESPIRATION AND FERMENTATION 251 



The oxidation processes therefore are not obscured by any external 

 features. Naturally then, the attention of botanists has been 

 continually directed to the study of the nature of this phenom- 

 enon, and it was in plant physiology that the question of the 

 internal chemistry of respiration has received special consideration. 



77. Methods of Studying Respiration. Intensity and Local- 

 ization of Respiration in Different Plants.— The methods of 

 studying respiration in plants are essentially methods of deter- 

 mining the exchange of gases between the plant body and the 

 atmosphere. Fundamentally, the method is identical with the 

 study of the gas exchange during photosynthesis. Generally, it 

 consists in placing a respiring plant or part of it in a hermetically 

 sealed container, which is provided with lateral tubes through 

 which from time to time samples of gas can be taken for analysis 

 by the same apparatus which is used in the study of photosynthesis. 

 Formerly, the eudiometric method, described in Art. 2, was em- 

 ployed also. All experiments with green plants or those which are 

 able to become green must, of course, be conducted in darkness, 

 lest the opposite process of absorption of carbon dioxide should 

 superimpose itself on respiration. 



Often, the study of respiration is confined only to the determina- 

 tion of the liberated carbon dioxide, which, of course, is more 

 readily made than is a complete gas analysis. For this purpose, 

 the respiring parts of a plant are placed in a container through 

 which is sucked an air current that has been cleared of carbon diox- 

 ide. Having passed over the plant, the air current leaves the car- 

 bon dioxide, caught on its way, in a special absorbing apparatus. 

 This may be either a U-shaped tube containing potassium hydrox- 

 ide or soda lime, or one of the various vessels containing potash. 

 The quantity of carbon dioxide formed per unit of time is esti- 

 mated by the increase in weight of the apparatus. Previous to 

 entering into the apparatus the current of air must be dried. Fre- 

 quently, a titrable solution of barium hydroxide is used as an 

 absorber of CO2, with Pettenkoffer's tubes used as a convenient 

 equipment (Fig. 101), through which an air current passes in the 

 form of fine bubbles which discharge to the barium hydroxide their 

 carbon dioxide. The quantity of the latter is determined by the 

 difference between the initial and final titration figures of the 

 solution. 



There is considerable variation between the intensity of respira- 



