212 PHYSIOLOGY OF NUTRITION 



during the period of darkness, so that respiration is at length retarded' because 

 of lack of material. When the plants are returned to the light the supply of 

 available carbohydrates is again increased and the respiratory process returns 

 to its usual rate. Such an interpretation finds further support in the observa- 

 tion that the change from darkness to light is accompanied by an acceleration 

 in the evolution of carbon dioxide only when the light contains the less refran- 

 gible wave-lengths (which are especially active in photosynthesis), and when the 

 surrounding air is supplied with carbon dioxide (without which photosynthesis 

 cannot occur). 



Bonnier and Mangin 1 state that there is also a direct influence of light upon 

 plant respiration, but that this is very slight. If plants are placed alternately 

 in darkness and in light a retarding effect of light is observed, and this bears 

 no relation to the photosynthetic process, since it is demonstrable in plants 

 without chlorophyll. The value of the respiratory ratio is independent of light. 



Maksimov 2 came to the conclusion that the effect of light upon the respira- 

 tion of Aspergillus niger varies with the age of the culture and with the nature of 

 the nutrient medium. He found that light exerted no influence upon the 

 respiration of young, well-nourished cultures, but that the respiration of old 

 cultures was increased by illumination. The stimulating effect became more 

 marked if the culture was deficient in nutrient material. Levshin, 3 however, 

 could observe no influence of diffuse light upon the rate of respiration in various 

 fungi. 



The partial pressure of oxygen in the surrounding atmosphere also influences 

 plant respiration. In this case, also, the value of the respiratory ratio does 

 not change. 



According to the results of Kosinski 4 and Palladin, 5 the concentration of 

 the nutrient solution exerts great influence upon the rate of respiration. If 

 plants are transferred from a more concentrated to a more dilute solution respira- 

 tion becomes more active, and a change in the opposite direction decreases 

 respiratory activity. Thus, ioo g. of etiolated bean leaves, with their petioles 

 dipping into a cane-sugar solution that was altered in concentration from time 

 to time, gave the following mean hourly rates of evolution of carbon dioxide, 

 for the different exposure periods. 



1 Bonnier, Gaston, and Mangin, Louis, Recherches sur la respiration des tissus sans chlorophylle- 

 Ann. sei. nat. Bot. VI, 18: 293-382. 1884. 



2 Maximow, N. A., lieber den Einfluss des Lichtes aud die Atmung der niederen Pilze. Centralbl. 

 Bakt. //, 9: 193-205. 261-272. 1902. 



3 Löwschin, A., Zur Frage über den Einfluss des Lichtes auf die Atmung der niederen Pilze. Beih. 

 Bot. Centralbl. 23: 54-64. 1908. 



4 Kosinski, Ignacy, Die Athmung bei Hungerzuständen und unter Einwirkung von mechanischen und 

 chemischen Reizmitteln, bei Aspergillus niger. Jahrb. wiss. Bot. 37: 137-204. 1902. 



5 Palladin, W., and Komleff, A., Influence de la concentration des solutions sur l'energie respiratoire et 

 sur la transformation des substances dans les plantes. Rev. gen. bot. 14: 497-516. 1902. 



о The respiratory activity of plant parts containing chlorophyll is of course difficult to 

 study as long as light is present, because of the fact that photosynthesis reverses the respira- 

 tion process, as far as the absorption of oxygen and the elimination of carbon dioxide is con- 

 cerned. In this connection, as well as with regard to the influence of light on respiration itself, 

 see: Spoehr, H. A., Photochemical processes in the diurnal deacidification of the succulent 

 plants. Biochem. Zeitsch. 57: 05-111. 1914. Idem, Variations in respiratory activity 

 in relation to sunlight. Bot. gaz. 59: 366-386. 1915. — Ed. 



