THE PHOTOSYNTHETIC PROCESS 61 



that chlorophyll affected the sensitiveness of the plastids which 

 contained it. 



The phenomenon of fluorescence has also been called upon to 

 explain the action of chlorophyll. The wave length in the fluores- 

 cence of chlorophyll is increased from that of green to that of red. 

 If the chlorophyll only had the power of shortening the wave 

 length from green to that of ultra-violet, then the ultra-violet 

 thus produced would be the effective light in making the formalde- 

 hyde and all would be clear. Unfortunately the organism does not 

 always conform to either our wishes or our hypotheses. 



The work of Willstatter, Baly, and others has made all these 

 previous explanations unnecessary. As seen from their equations, 

 chlorophyll is primarily neither a screen, a sensitizer, nor a trans- 

 former of wave lengths. It takes a prominent part in the series of 

 chemical reactions in the chain of events which results in the 

 production of the formaldehyde. It is a kind of light-energized 

 catalyst, and takes a direct part in the chemical changes during 

 which a large part of the energy represented by the carbohydrate 

 products is absorbed. Its chief role is chemical, but this does not 

 preclude the possibility that it may also act as an absorbing screen, 

 which it certainly seems to do. 



Part Played by the Carotinoids. — As seen from the equations 

 of Baly, carotin and xanthophyll both have an important role in 

 photosynthesis. Chlorophyll B contains more oxygen than A, and 

 xanthophyll contains more than carotin, which facts are related 

 to the series of oxidations and reductions found to take place. 

 Carotin reduces chlorophyll B and becomes xanthophyll. A reduc- 

 ing enzyme then changes xanthophyll back to carotin and the 

 freed oxygen is evolved. This oxygen comes originally from the 

 carbon dioxide that united with chlorophyll A to form B and 

 formaldehyde; while the carotin then changes B back to A by 

 removing the excess oxygen. This continuous process thus results 

 in the intake of carbon dioxide and the evolution of oxygen. The 

 reader must be warned again, however, that these equations are 

 purely theoretical and that we are forced to admit that at the 

 present time we are not at all sure on these points. 



The Condensation Process and the First Sugar Formed.— Just 

 how much of the synthesis of carbohydrate material is photosyn- 

 thesis and how much is independent of light has not yet been 

 determined, but the suggestions of Willstatter, Warburg, and 



