DAM EL I. ARNON 493 



T2I3-3, Sogof b«*t 



30' L 



C,s, ADP.TPN.FMN 



OWYDROXYACETONE 

 =1^^ PHOSPHOGLYCERATE 



PHOSPHATE 



fi 



* 



MONOPHOSPHATES 

 (GLUCOSE, FRUCTOSE) 



OPHOSPHATES 

 (FF?UCTOSE,R!BU_OSE) 



X 



FMEM0L/«I»TEJ1- 



Fig. 1. Products of CO. assimilation by illuminated chloroplasts isolated 

 from sugar beet leaves. (VVhatley, Allen, Trebst and Arnon, 175). 



assimilation and could therefore subsist only by consuming the organic 

 substances formed by the photosynthetic group. 



So firm was the conviction that only green plants could form or- 

 ganic substances by assimilating CO2 that in the 19th century the 

 term "assimilation" became established in several European languages 

 to describe what is now called photosynthesis. Assimilation, i.e., the 

 formation of organic substances from COo, was believed to be peculiar 

 to green plants, whereas metabolism, i.e. the utilization of organic 

 substances formed by plants, occurred in both plants and animals 

 (67). 



This seemingly logical and orderly division of the living world was 

 destroyed by two discoveries in the 1880's. Winogradsky (178, 179) 

 discovered chemosynthetic bacteria, i.e., cells without chlorophyll that 

 could form their cellular substance by assimilating COo in the dark. 



