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TEXTBOOK OF PLANT PHYSIOLOGY 



formation of one kind of chemical energy into another, is called 

 "chemosyn thesis." These bacteria will be discussed in detail in 

 Chap. VIII, where other oxidation processes in plants are consid- 

 ered. Though these bacteria, especially the nitrifying ones, are 

 of common occurrence in nature, they constitute but a small part 

 of the total mass of organic matter. Therefore, it may be said 

 with certainty, that almost all of the organic matter found on the 

 earth's surface has been created by means of radiant solar energy. 

 9. Relation of Chlorophyll to Absorption of Light Energy. 

 Optical Properties of Chlorophyll. Internal Chemistry of Photo- 

 synthesis.— To be utilized in the process of photosynthesis, the 



700 B C 



E 500F 



G >oo 



700B C 



600D 



E 5ooF 



f-00 



FlQ 9. __ Absorption spectrum of chlorophyll. Above, chlorophyll, a; below, 

 chlorophyll, b (after Willstaltcr and Stoll). 



energy of light, in the first place, must be absorbed by a screen 

 at least partly opaque and afterwards transformed into chemi- 

 cal energy. Chlorophyll is a substance with such a property. 

 It absorbs light, not as a whole, however, but selectively. When 

 the solar spectrum is passed through a chlorophyll solution, it is 

 seen that separate portions of the spectrum are absorbed by it, 

 while others are transmitted, though weakened in different 

 degrees. In this manner the absorption spectrum of chlorophyll 

 is obtained (Fig. 9). 



The most intense absorption takes place in the region of the 

 red rays, between the Frauenhofer lines B and C (wave-length 730 

 to 650mm)- An almost equally intensive absorption will be found 

 in the blue-violet portion of the spectrum, to the right of line F 

 (470mm)- In addition to these, several other less distinct absorp- 

 tion bands may be detected. The absorption spectra of chloro- 



