I H. A. SPOEHR 



reduction of carbon dioxide and the course of sugar synthesis 

 in the green leaf. On the part of the chemist these attempts 

 have been largely of a purely speculative nature, and some of the 

 hypotheses proposed unfortunately show a lamentable lack of 

 knowledge of the conditions under which photosynthesis takes 

 place, as well as of the physiology and structure of the chloro- 

 phyllous cell. Probably largel}^ for these reasons few of the sug- 

 gestions offered by the chemists received any serious attention 

 from the botanists, there being at the time few plants physiolo- 

 gists with sufficient training in or even sympathy with the chemical 

 aspects of these problems. 



The great success of the general method of synthesis in organic 

 chemistry influenced the work in this field to a considerable 

 extent, as is evidenced by the large number of attempts at extra- 

 cellular photosynthesis. Some have fallen into the error of 

 reasoning, that if they can produce sugar, or the substances 

 closely related to sugar, from carbon dioxide and water, by 

 almost any means, that this is necessarily also the process taking 

 place in the leaf. 



It can safely be said at the outset that, when critically con- 

 sidered from a physiological view point, none of the existing 

 theories is even moderately well established by observation of 

 facts. 



The theory which in recent years has received most promi- 

 nence is that suggested by Baeyer^ in 1870. In a paper entitled 

 "Ueber die Wasserentziehung und ihre Bedeutung fiir das Pflan- 

 zenleben und die Gahrung," Baeyer discusses the various ways of 

 splitting off of water and subsequent condensation of organic 

 compounds. In 1861 Butlerow^ had discovered that formalde- 

 hyde, in aqueous alkaline solution, condenses to an optically 

 inactive syrup, possessing some of the properties of hexose 

 sugars. Baej^er considers formaldehyde in aqueous solution to be 

 CH2(OH)2 and that the Butlerow condensation is simply one 



^ Baeyer, A., Ueber die Wasserentziehung und ihre Bedeutung fiir das Pflan- 

 zenleben und die Gahrung. Ber. deut. Chem. Ges. 3: 63-78, 1870. 



^ Butlerow, A., Bildung einiger Zuckerarten durch Synthese. Ann. der Chem. 

 (Liebig) 120:295-98, 1861. 



