2 26 PHYSIOLOGY OF NUTRITION 



carbon dioxide in the air when they have been previously kept for a time in 

 an atmosphere free from oxygen. This fact has been mentioned before, but the 

 following example will make it clearer. 



Of two portions of frozen, etiolated bean leaves, one portion was exposed 

 to the air for sixty-three hours and the other was first exposed for twenty-three 

 hours to an atmosphere of hydrogen, and then to the air for forty hours. The 

 first portion (in air for sixty-three hours) gave off 286 mg. of carbon dioxide. 

 The second portion gave off 183 mg. of carbon dioxide during its twenty-three 

 hours in hydrogen and 245 mg. during the succeeding forty hours in air, or 428 

 mg. during the entire sixty-three hours. During the whole period the second 

 portion gave off 50 per cent, more carbon dioxide than did the other. In the 

 first portion (in air all the time) the respiration pigments removed a part of the 

 active hydrogen produced by the first stage of anaerobic respiration, and there- 

 fore exerted the same retarding influence upon the process as was evident in 

 the experiments of Palladin and Lvov (see page 207), in which the chromogen 

 of the beet or methylene blue retarded alcoholic fermentation. In considering 

 plant respiration it is thus necessary to distinguish between the hydrogen that 

 is normally taken up by the hydrogen acceptor and is then oxidized to form 

 water, and the other, more active, hydrogen that is simultaneously being pro- 

 duced by the anaerobic reactions under the influence of reductase, as in the 

 formation of alcohol by reduction. This latter hydrogen is necessary for the 

 continuation of the anaerobic process. 



As has been stated previously (pages 213), the respiration process is accel- 

 erated by wounding. Krasnosselskaia 1 has shown that this acceleration is con- 

 comitant with an increase in the amount of anaerobic enzymes (such as zymase, 

 perhaps) and also with an increase in the amount of peroxidase present in the 

 tissues. Four equal portions of leek bulbs that had been wounded and allowed 

 to remain alive for one, four, seven and fifteen days, respectively, were finally 

 frozen and treated with pyrogallol and hydrogen peroxide. The four portions 

 produced 25.2, 74.8, 149.6, and 200.4 m g- or carbon dioxide, respectively, which 

 indicates the progressive increase in the amount of respiration enzymes in the 

 wounded bulbs. 



Poisons also accelerate plant respiration (see page 213), but without increas- 

 ing the respiration enzymes. 2 Two similar lots of etiolated stems of Viciafaba 

 were kept in darkness for some time, with their cut ends in sugar solution. One 

 lot was then treated with quinin, and produced 21.4 mg. of carbon dioxide in 

 two hours, while the lot without the alkaloid formed only n 3 mg. Both lots 

 were then killed by freezing. After thawing, the one with quinin produced 37.2 

 mg. of cabon dioxide in twenty-five hours, while the other formed 37.6 mg. A 

 very'marked acceleration in the evolution of carbon dioxide is seen to have been 



1 Krasnosselsky, T., BiHung der Atmungsenzyme in verletzten Pflanzen. Ber. Deutsch. Bot. Ges. 

 23:142-155. 1905. Idem, Bildung der Atmungsenzyme in verletzten Zwiebeln von Allium cepa. Ibid. 

 24: 134-141. 1906. 



- Palladin, V. I. [W.], Respiration des plantes comme somme des proces de fermentation. [Russian. 

 Mem. Acad. Imp. Sci. St.-Petersbourg VIII, 20 5 : 1-64. 1907. Idem, sur Taction des poisons sur la respira- 

 tion des plantes. [Russian.] Bull. Acad. Imp. Sci. St.-Petersbourg VI, 4: 401-421- tgio. [This is also 

 reported in the reference given in note 3. p. 213.] 



