THE CHEMICAL PROCESSES IN PLANT RESPIRATION IIQ 



as assumed by Wieland is the transformation of acetaldehyde 

 according to the Cannizzaro reaction: 



2CH3— CHO = CH3— CO— 0— CH.,— CH3 

 CH3— CO— O— CHo— CH3 + HoO = CH3— COOH 



+ CH3— CHoOH. 



The ethyl alcohol again changes to acetaldehyde and finally 

 all the alcohol may change to acetic acid. 



From the preceding exposition it is evident that the removal 

 of hydrogen from the aldehyde hydrates is unlikely, so much 

 the more so because demonstrable aldehyde peroxides are 

 formed as intermediate products with access to oxygen. To all 

 appearances entirely different processes take place with the 

 exclusion of oxygen than with access to oxygen: aldehydes 

 change to alcohols and acids according to Cannizzaro. 



These objections do not have the effect of setting aside the 

 Wieland theory. They only go to show that in some cases the 

 Bach-Engler theory deserves the preference. In the case of 

 biological oxidation processes there is probably hydrogen 

 activation as well as oxygen activation. In some cases the 

 oxidation proceeds according to the Bach-Engler scheme, but 

 in other cases according to that of Wieland. 



3. THE RESPIRATORY MATERIAL 



The fermentable sugars serve as the respiratory material 

 of plants. This fact has been proven for seed-plants by means 

 of a large number of unequivocal experimental results. Bous- 

 singault^ has shown by means of numerous analyses of the 

 elements that carbohydrates in particular disappear during the 

 respiration of germinating plants. Borodin- showed that leafy 

 shoots respire more energetically after an exposure to Ught, a 

 condition which is doubtless due to the formation in the light 

 of respiratory material in the form of carbohydrates. Palladin^ 

 proved that etiolated bean leaves, which contain very small 

 amounts of soluble carbohydrates, respire much more energeti- 



' Boussingault, J. B. Agronomie, chimie agncole et physiol. 4: 245. 1868. 



2 Borodin, J. Physiol. Untersuch. uber die Atmung der Laubsprosse. 1876. Russian. 



3 Palladin, W. Rev. gen. de hot. 5: 449. 1893:6:201. 1894:13:18. 1 90 1 ; and others. 



