CHAPTER 1 



Introductory Remarks 



§ 1 The Over-all Reaction 



The Dutch physician and chemist Ingen-Housz (22) was the first to deter- 

 mine in 1772 that the production of oxygen ("vital air") by the green plant 

 under the influence of light is dependent upon the green parts of the plant. 

 Priestley (30) and van Barneveld (2) had made similar observations in- 

 dependently at about the same time. Other earlier investigators, whose 

 writings were, however, less precise, were Bonnet and Hales. The name 

 chlorophyll was given to the green substance of the leaves by Pelletier and 

 Caventou (29) in 1818. De Saussure (33) in 1804 depicted the over-all 

 reaction of Oo production as follows: 



light 

 CO2 + H2O — ^ organic substance + O2 



He found that the ratio of the COo consumed and the O2 produced was equal 

 to 1. 



To-day this type of COo-assimilation is called photosynthesis, as there are 

 many other types of C02-assimilation without the absorption of radiation 

 energy. Sachs (31) showed in 1868 that chlorophyll is indispensable for 

 photosynthesis. In 1881 Engelmann (11) succeeded in isolating the chloro- 

 phyll-containing particles — the chloroplasts — from various plants. He was 

 able to show that these isolated chloroplasts develop O^ when illuminated 

 (see § 48). 



The chemical nature of chlorophyll remained obscure until the funda- 

 mental work of Willstatter and Stoll (47) was published. Conant (6, 7) and 

 especially H. Fischer (12) largely contributed to our present knowledge of 

 the chlorophyll molecule. 



To-day the reaction equation of photosynthesis is written as follows: 



light 

 CO2 + H2O -^ — > (CH2O) + O2 - 112000 cal 



The reaction is endothermic. The product (CH2O) indicates a non-defined 

 primary substance of the carbohydrate group. Production of O2 and fixation 

 of COo are characteristic of the photosynthetic reaction. For every molecule 

 CO2 reduced one molecule Oo is produced. The ratio 7 = COo/Oo is 

 called the assimilatory or photosynthetic quotient. Theoretically it equals 1. 

 In reality this need not be the case, as CO2 can be partly reduced without 



3 



