234 THE CARBOHYDRATES 



the suberin walls are insoluble in all fat-solvents, and do not 

 melt at a temperature below 290° C. 



An investigation of the chemical nature of potato cork was 

 undertaken by Rhodes,* who obtained a chloroform extract 

 and an insoluble residue ; the latter boiled with excess of 

 alcohohc soda gave a solution from which he separated normal 

 and hydroxy-acids, the latter being characterized by insolu- 

 bility in light petroleum. The hydroxy-acids are not extracted 

 from the suberin lamella until after saponification, showing 

 that they occur there in some form of combination. He 

 concludes that the suberin lamella arises by changes taking 

 place in the fatty material rendering them no longer soluble 

 in fat solvents ; part of the fatty substances never undergo 

 this change, and it is this part which is chiefly responsible for 

 the staining properties of the lamella with the ordinary fat 

 stains. The lamella consists in the main of relatively insoluble 

 normal and hydroxy-fatty acid complexes which can be re- 

 leased by prolonged saponification as soluble soaps. Glycerol 

 was found only in the chloroform extract and then only in 

 traces, except in the case of regenerated cork layers. 



Microchemical Reactions of Suherized and Cuticularized 



Memhrayies. 



1. With chlorzinc iodide, and also with iodine and sul- 

 phuric acid, a brown or yellow colour is given. 



2. Suberized and cuticularized walls are insoluble in 

 cuprammonia and concentrated sulphuric acid. 



3. Suberized walls are coloured yellow with strong potash 

 solution ; on heating the colour deepens, and on boiling 

 yellow oily drops exude from the membranes. 



4. Suberized walls are the most resistant of membranes to 

 Schultze's macerating mixture. 



5. These membranes are stained red by treatment with 

 alcohohc solutions of Alkannin, Sudan HI and Scharlach R. 



6. If a section of the material be treated first with eau de 

 Javelle, in order to destroy any tannins which may be present, 



* Rhodes : " Biochem. Journ.," 1925, 19, 454. 



