XXXI 



THE LIGHT FACTOR IN PHOTOSYNTHESIS 



H. A. Spoehr and J. H. C. Smith 



Carnegie Institution of Washington, Division of Plant 

 Biology, Stanford University, California 



The role of light in the formation of the chloroplast pigments: Chlorophyll — Caro- 

 tenoids. The optical properties of leaves. Optical properties of the chloroplast pigments. 

 Effect of light intensity in photosynthesis: Inhibition by high light intensities — Nutri- 

 tional factors — Chemical inhibitors — Temperature — Light and internal factors; Water, 

 Chlorophyll — Light intensity and morphological factors — Time effect in photosynthesis — 

 Compensation points — The limits of light intensity utilizable in photosynthesis — Effect 

 of wave-length on photosynthetic rates; Infra-red, visible, ultra-violet — Wave-length limits 

 of photosynthesis. The mechanism of the photosynthetic reaction. The energy relations of 

 photosynthesis: The apparent efficiency of the photosynthetic process — The real efficiency 

 of the photosynthetic reaction — Energy transfer. Photosynthesis in bacteria: Purple 

 sulfur bacteria. References. 



In this survey the discussion is confined as closely as has been possible 

 to those aspects of the phenomenon of photosynthesis which are primarily 

 concerned with the influence of light. Of necessity, even such a restricted 

 discussion involves a wide range of physical and chemical concepts and 

 naturally demands some knowledge of fields which are ancillary to the 

 central theme. It has obviously not been possible to give consideration 

 to all the work which has been done in this field. This is especially 

 true of the older publications. The aim has been to describe the present 

 status of the subject with some consideration of the background offered 

 by the older work. For a discussion of this reference is made to the 

 following monographs : H. Schroeder, Die Hypothesen liber die chemischen 

 Vorgange bei der KohlensaUre-Assimilation und ihre Grundlagen, Jena, 

 1917; J. Holluta, Die neueren Anschauungen uber die Dynamik und 

 Energetik der Kohlensaureassimilation, Stuttgart, 1926; W. Stiles, 

 Photosynthesis, The assimilation of carbon by green plants, London, 

 1925; H. A. Spoehr, Photosynthesis, New York, 1926. 



THE ROLE OF LIGHT IN THE FORMATION OF THE CHLOROPLAST 



PIGMENTS 



CHLOROPHYLL 



It is very generally agreed that chlorophyll is essential for photo- 

 synthesis. Although this fact has not been demonstrated with the 

 complete certainty desirable for such an important conclusion, as yet no 

 evidence has been presented contrary to the assumption that the plant 



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