24 



PHYSIOLOGY OF NUTRITION 



C, in the orange, in the yellow, and in the green. At the conclusion of the 

 experiment analyses of the gas were made, by means of a very sensitive appa- 

 ratus capable of measuring extremely small amounts 

 of gas. Timiriazev's results are graphically repre- 

 sented in Fig. 13. The ends of the five ordinates, for 

 the five positions in the spectrum where the tubes were 

 exposed, are joined to form a curve, which represents 

 the relative rates of decomposition of carbon dioxide 

 in these different regions of the spectrum. The maxi- 

 mum decomposition occurs in the red, between B and 

 C, in the region where light is most strongly absorbed 

 by chlorophyll. No decomposition occurs between A 

 and B (the line m represents the amount of carbon 

 dioxide eliminated during the experiment). These 

 results were confirmed by Engelmann 1 and Reinke. 2 

 Engelmann was the originator of the bacterial 

 method for the study of photosynthesis. It is well 

 known that many bacteria are active only in the 

 Fig. 13. — Graphs showing presence of oxygen, and that their movement ceases 



relative rates of decomposi- ,1 TJ . £l 



tion of carbon dioxide in as soon as there ls no oxygen present. If a filament 

 different parts of the spec- of a green alga is placed in a culture of such bacteria, 



trum. (After Timiriazev.) i.j j - £ ,1 ... 11 



upon a slide, and it the preparation is protected by a 



a,B C D 



Eb 



Fig. 14. — Bacterial movement in the regions 

 of the absorption bands of chlorophyll. (After 

 Englemann.) The dots indicate moving bacteria 

 and the letters denote the Fraunhofer lines. 



700 600 500 VOO 



Fig. 15. — AB, distribution of heat 

 energy in the solar spectrum. (After 

 Langley.) 100-14, relative rates of car- 

 bon-dioxide decomposition by leaves in 

 red and in blue light. 



cover glass and darkened, the movement of the bacteria eventually ceases 

 because of lack of oxygen. If a solar spectrum is now projected upon the alga 



1 Engelmann, Th. W., Ueber Sauerstoffausscheidung von Pflanzenzellen im Mikrospectrum. Bot. 

 Zeitg. 40: 419-426. 1882. 



2 [Reinke, J., Untersuchungen uber die Einwirkung des Lichtes auf die Sauerstoffausscheidung der Pflan- 

 zen. II. Die Wirkung der einzelnen Strahlengattungen des Sonnenlichtes. Bot. Zeitg. 42: 17-29, 33-46, 

 49-59- 1884. See column 27. Idem, Die Zerstorung von Chlorophyllosungen durch das Licht und eine 

 neue Methode zur Erzeugung des Normalspectrums. Ibid. 43: 65-70, 81-89, 97-101, 113-117, 129-137. 

 1885. See column 84. Idem, Die Abhangigkeit des Ergrunens von der Wellenlange des Lichts. Sitz- 

 ungsber. (Math. Naturw. Mitth.), K. Preuss. Akad. Wiss. Berlin. 1893 : 301-314. 1893.] 



