26 PHYSIOLOGY OF NUTRITION 



the light rays between lines B and C. But when other pigments besides chloro- 

 phyll are present the maximum of this decomposition may fall in another part 

 of the spectrum.^ In the Cyanophycese the maximum occurs at D; the brown 

 algae show a maximum between D and E, although the decomposition between 

 B and C is here almost as great; finally, the red algae have a maximum between 

 D and E also, but the decomposition between B and C is here very weak. 

 These facts are in agreement with the distribution of the various algae, accord- 

 ing to depth, in the ocean; while the surface layer of water is mainly inhabited 

 by green algae, the red forms are found at very great depths. Spectroscopic 

 investigations have shown that red light, which is essential to green algae, is 

 quickly absorbed by water and that this light is entirely absent at no great 

 distance below the surface. On the other hand, the green and blue rays, which 

 are absorbed by the red algae, attain great depths. 



According to Engelmann,^ plants that contain no chlorophyll may also 

 decompose carbon dioxide, provided they contain another pigment; as, for in- 

 stance, the purple bacteria. ^ 



Engelmann's theory of complementary pigments found confirmation in the 

 interesting researches of Gaidukov' upon the influence of colored Ught upon 

 the color of Oscillaria. This alga tends to assume the color complementary to 

 that of the light acting upon it, and the longer the organism remains in the 

 colored light the more pronounced is the response. The following kinds of 

 illumination produced the following colorations in the organism. 



Color of Light Color of Alga 



Red Green 



Brownish-yellow Blue-green 



Green Reddish 



Blue Brownish-yellow 



The principle illustrated by this phenomenon was designated by Gaidukov as 

 the law of complementary chromatic adaptation. 



The amount of light* necessary for the decomposition of carbon dioxide is 

 closely related to the individual properties of the plant, some forms needing 



' Engelmann, Th. W., Farbe und Assimilation. Bot. Zeitg. 41: 1-13,17-29, 1883. 



2 Engelmann, Th. W., Die Purpurbacterien und ihre Beziehungen zum Licht. Bot. Zeitg. 46 : 661-669, 

 677-689, 693-701, 709-720. 1888. 



» Gaidukov, N., Ueber den Einfluss farbigen Lichts auf die Fftrbung lebender Oscillarien. Abh. K. 

 Preuss. Akad. Wiss. Berlin, 1902. Anhang, Phys. Abh. V., p. 1-36. 



« Kreusler, U., Ueber eine Methode zur Beobachtung der Assimilation und Athmung der Pflanzen und 

 fiber einige diese Vorgftnge beeinflussende Momente. Landw. Jahrb. 14:. 913-965. 188s. Timriazeff, 

 C, Bur le rapport entre I'intensitS des radiations solaires et la decomposition de I'aoide carbonique par les 

 v6g«taux. Compt. rend. Paris 109: 379-382. 1889. Pantanelli. Enrico, Abh&ngigkeit der SauerstofF- 

 ausscheidung belichteter Pflanzen von ausseren Bedingungen. Jahrb. wiss. Bot. 39: 167-228. 1904. 

 Lubimenko, W., Sur la sensibility de I'appareil chlorophyllien des plantes ombrophiles et ombrophobes. 

 Rev. gfo. Bot. 17: 381-415. I90S- Idem, concentration du pigment vert et I'assimilation chlorophyl- 

 lienne. Ibid. 20: 162-177, 217-238, 253-267, 285-297. 1908. Idem, Production de la substance s^che 

 et de la chlorophylle chez les v«g6taux supSrieurs aux difflSrentes intensit6s lumineuses. Ann. sci. nat. 

 Bot. IX, 7: 321-415. 1908. 



p But Molisch's studies have shown that the purple bacteria contain chlorophyll and that 

 the purple pigment plays no direct part in their photosynthetic process. See: Molisch, Hans, 

 Die Purpurbakterien nach neuen Untersuchungen, eine mikrobiologische Studie. 92 p. Jena, 

 1907. — Ed. 



