I] INTRODUCTION 7 



Another line of syntheses is that which leads to the production of 

 the fats and allied substances. The fats are mainly glycerides of acids 

 of the methane and olefine series, such as butyric, palmitic and oleic 

 acids. Like all other plant products the fats must either directly or 

 indirectly arise from the carbohydrates. There is evidence that the 

 origin is fairly direct, as, for instance, in fatty seeds when the fats take 

 the place of sugars in ripening. The sugars, as we know, are aldehydes 

 of the polyhydric alcohols of the methane series. It has been suggested, 

 though the actual stages have not been ascertained, that by various 

 oxidation and reduction processes, the sugars yield fatty acid residues 

 which then condense to form the fatty acids of high molecular weights 

 present in fats. By a converse process, the fats, especially when they 

 are stored as reserve materials in seeds, are broken up, and sugars are 

 again formed which pass to other parts of the germinating seedling, and 

 are there used in other synthetic processes. 



A third main line of syntheses is that which gives rise to the aro- 

 matics of the plant. Since no ring compound is absorbed by the green 

 plant, it follows that by some process the aliphatic structure must be 

 transformed into the aromatic. Thus, for instance, the trihydric phenol, 

 phloroglucinol, might at some stage be formed from a hexose by conversion 

 of the aliphatic chain into a closed ring : 



OH H OH OH 

 OHO— C— C— 0— C— CH2OH — 3H2O = CO— CH2— CO— CH2— CO— CH2 

 H OH H H I I 



Glucose 



H2 H 



OC CO HOC COH 



= 11= II I 



H2C CH2 HC CH 



\c/ \c/ 



O OH 



Phloroglucinol 



There is evidence that aromatic compounds, such as phloroglucinol, 

 tannins, flavones and anthocyanins are synthesized in the leaves, and that 

 sugar-feeding, by floating leaves in sugar solutions, leads to the increase 

 of aromatics in the tissues. When the ring structure has been once 

 synthesized, further changes can take place either by the addition of 

 side-chains to the ring or by the condensation of two or more rings. In 

 this way the great multitude of aromatic products present in the higher 

 plants may arise. 



