THE THEORIES OF PHOTOSYNTHESIS 3 



of water loss and condensation of six rH2(OH)2 molecules. 

 6 CH2(OH)2 -6H20-^COH(C(OH)H)4CH,OH. 



Baeyer then suggests that this may be the way in which grape 

 sugar is formed in the plant. The idea of the similarity of chloro- 

 phyll and haemoglobin was prevalent at the time; it seemed there- 

 fore likely that chlorophyll should also fix CO. The sunlight 

 splits the CO2 into CO and O, the oxygen escapes, and the car- 

 bon monoxide, held by the chlorophyll, is reduced to formalde- 

 liyde, CO+H2— >C0H2, which is then condensed to sugar. This 

 is the substance of the Baeyer hypothesis, formulated without 

 the support of experimental evidence, it was given as a mere 

 suggestion. In recent years this hypothesis has largely directed 

 the course of the investigations in this subject, and, it seems 

 to the writer, to the detriment of critical and independent 

 thinking on the broader aspects thereof. 



The fact which more than any other gave strength to this 

 theory, and which is the underlying principle of the whole idea, 

 was the discover}^ of Butlerow. This discovery was elaborated 

 by O. Loew,'' who gave the name formose to the sugar mixture, 

 and especially by Emil Fischer,^ who prepared therefrom some 

 of the sugars found in nature. 



Although the conditions under which formose is formed from 

 formaldehyde in vitro have been carefuU}^ worked out, this phase 

 of the question has received no attention from the plant physiolo- 

 gists; we have no definite idea whether the conditions of solution 

 in the chloroplasts are such under which condensation of for- 

 maldehyde takes place. We shall return to this subject later. 



There are three main points which immediately arise on con- 

 sidering the Baeyer hypothesis, and the experiments that have 

 been applied have been directed in these three different, though 

 interrelated courses. From the very extensive nature of the sub- 

 ject some of the investigations have reached out far into other 



' Loew, O., Ueber Bildung von Zuckerarten aus Formaldeh3'd. Ber. deut. 

 Chem. Ges. 22 : 470-78, 1889. 



^ Fischer, Emil, Ueber die Verbindungen des Phenylhj'drazins mit den Zucker- 

 arten. Ber. deut. Chem. Ges. 21:988-91, 1888. Bildung von Acrose aus For- 

 maldehyd. Ibid 22: 359-60, 1889. 



