THE PECTIN GBOUP. 201 



These groups remain in combination with the original cellulose 

 as ligno-cellulose. 



The same authors hold that the cellulose of cereal-straws, 

 esparto grass, &c., is not normal cellulose, but oxy-cellulose. 

 These substances contain more oxygen than cellulose, and 

 probably CO groups. They yield furfurol on treatment with 

 hydrochloric acid and give a characteristic rose-red colour on 

 treatment with solutions of aniline salts. The name hemi- 

 cellulose has been proposed for another class of cellulose, which 

 occurs in many plants and which differs from ordinary cotton 

 cellulose in being much more readily hydrolysed both by acids 

 and by enzymes. 



Pectin Substances. This is the name given to the co- 

 agulable substances present in many fruit juices, stems, roots, 

 &c. They are generally said to contain more oxygen in pro- 

 portion to hydrogen than is present in a true carbohydrate, 

 but according to Tromp, de Haas, and Tollens,* who analysed 

 specimens of pectin derived from apples, cherries, rhubarb, 

 currants, plums, and swedes, the ratio of oxygen to hydrogen 

 does not differ materially from the number (8 : 1) observed in 

 true carbohydrates. The percentage of carbon varies from 

 41 to 45 %. Pectins by hydrolysis yield pentoses and hexoses. 

 Tollens regards them as consisting of carbohydrates in union 

 with acids. 



Pectose is the parent member of the group ; it occurs 

 associated, or perhaps combined, with the cellulose as pecto- 

 cellulose, and is insoluble. It is particularly abundant in 

 unripe fruits. 



Pectin, a product of the hydrolysis of pectose, is soluble in 

 water and yields solutions which readily gelatinise. It is 

 produced during the ripening of fruits, &c., hydrolysis being 

 brought about either by the vegetable acids present or by an 

 enzyme known as pectase. 



By further hydrolysis, effected by boiling water or alkalies, 

 metapectin, parapectic acid, and -pcctic acid are produced. The 

 exact composition of these substances has not been determined, 



* Annalen 1895, S86, 278. 



