316 PLANT PHYSIOLOGY 



bines with water rather than with free oxygen, and oxidation is 

 thus seen to be a kind of hydrolysis. 



These same steps are thought to be found in animal respiration 

 as well as in plants. Here the process is made more complicated 

 by the special system (the blood with its red corpuscles) which 

 carries the oxygen from the exterior (lungs) to the tissues. The 

 hemoglobin when united with oxygen becomes red oxyhemo- 

 globin, and when deprived of its oxygen is the bluish hemoglobin 

 of venous blood. 



Palladin saw in plant pigments such as some of the glucosides, 

 anthocyans, and the natural plant dyes which vary in their color 

 with the state of oxidation, an apparatus similar to hemoglobin. 

 Many of these, like methylene blue, are colored when oxidized 

 and colorless when reduced. According to this conception, the 

 steps in respiration where these pigments or " respiratory chromo- 

 gens" (also called phytohematins) are concerned, are as follows: 



R (pigment) +H 2 = RH 2 (colorless chromogen) 

 12RH 2 +60 2 = 12H 2 + 12R(pigment) . 



The pigment is thus regenerated and water and carbon dioxide 

 are the ultimate products formed. 



If the chromogens are merely " hydrogen acceptors," the entire 

 scheme, which employs the oxidases of Bach and Chodat as well 

 as the respiration pigments of Palladin, may then be represented 

 as follows : 



C 6 H 12 6 +6H 2 = 6C0 2 + 12H 2 



12R+12H 2 =12RH 2 



A (oxygenase) +0 2 (molecular oxygen from air)=A0 2 

 (peroxide) 



A0 2 (under influence of peroxidase)— >A+ O+O (acti- 

 vated) 



12RH 2 +60 2 = 12R+ 12H 2 



Summary: C G Hi 2 6 +60 2 = 6C0 2 +6H 2 0. 



Inasmuch as the oxygenase takes the oxygen from the air rather 

 than from the pigment, and since there seems to be no necessity 

 for oxygen carriers in plants as in animals, the advantages of such 

 a scheme are limited to the certain cases where the chromogens 

 are known to occur. 



Sufficient has been said, however, to impress the student with 



