PECTINS 



203 



to a solution of the middle lamella ; a somewhat similar effect 

 was shown by Brown * to occur when an enzyme extract of 

 Botrytis cinerea was allowed to act upon tissues of potato, 

 turnip, beet, and apple. It was, moreover, shown by Wino- 

 gradsky f that the retting of flax was due to the solution of 

 pectic substances by enzymes secreted by bacteria. 



Origin and Constitutional Relationships of the Pectins. 



The fact that galacturonic or similar sugar aldehyde acids 

 occur in pectins, hemicelluloses, and gums suggests that all 

 cell wall constituents are more or less related to each other. 

 It must be borne in mind that whilst the cell wall of un- 

 lignified elements is composed of cellulose together with 

 pectin, in hgnified elements lignin occupies the place of 

 pectin ; for this reason pectin is regarded as the precursor 

 of lignin, and the fact that both pectins and lignin contain 

 acetyl % and methoxyl groups would tend to support this 

 view. Ehrhch § even claims to have isolated from the lignified 

 tissues of the flax plant a substance which he describes as a 

 resin-Hke lignic acid ; this he considers to represent a tran- 

 sition stage between a typical unaltered pectin and lignin. 

 Fuchs II considers that lignin may have been produced from 

 pectins by loss of water and oxygen. 



It has been suggested by Nanji, Paton, and Ling that 

 pectins themselves arise from the condensation of galactose 

 to a hexagalactan which is then oxidized to uronic acids and 

 methoxylated. 



Yet another suggestion is that of Smolenski,^ who regards 

 pectins as intermediate stages in the conversion of hexoses 

 into pentoses. 



The Changes taking Place in Ripening. 



The view originally put forward by Fremy was that 

 softening of the tissues of fruits on ripening was due to a 



* Brown : " Ann. Bot.," 1915, 29, 313 ; 1917, 31, 489. 



t Winogradsky : " Compt. rend.," 1895, 131, 742. 



X But see also Nelson : " J. Amer. Chem. Soc," 1926, 48, 2945. 



§ Ehrlich : " Zeit. angew. Chem.," 1927, 40, 1305. 



II Fuchs : " Brennstoflf Chem.," 1926, 7, 302. 



^ Smolensk! ; " Chem. Soc. Abstracts," 1924, i, 16. 



