SUBERIN 233 



In addition to this normal formation of cork, a phellogen 

 may arise and form cork as a result of wounding, and suberi- 

 zation, without the formation of a phellogen, may take place 

 when non-superficial cells are exposed by the removal or 

 destruction of superficial tissue. Further, cork formation is 

 associated with the fall of the leaf. 



A mature cork cell consists of an internal suberin lamella 

 possessed of fat-staining properties, a cellulose layer and a 

 middle lamella both of which are more or less impregnated 

 with fat-like bodies to which the name of suberin is given 

 and to which is due the characteristic properties of cork, 

 more especially relative impermeability to water and to air. 



It was formerly thought that cork was a compound of 

 cellulose and suberin. The work of Gilson,* however, shows 

 that cellulose does not enter into the composition of cork for 

 the following reasons : — 



1. Cellulose is not attacked by prolonged boiling in a 

 3 per cent solution of potassium hydrate in alcohol ; suberized 

 walls, on the other hand, are dissolved. 



2. Phellonic acid (C22H43O3) has been isolated from cork, 

 and this substance, together with its potassium salt, gives a 

 red coloration with chlorzinc iodide. This suggests that the 

 coloration of suberized membranes with chlorzinc iodide after 

 treatment with potash is due to the presence of potassium 

 phellonate and not to cellulose, for, in addition, the coloration 

 does not take place if the corky tissue be subjected to the 

 action of boiling alcohol after treatment with potash. 



3. After treatment with cuprammonia, the chlorzinc iodide 

 gives a yellowish-brown colour ; this, according to Gilson, is 

 due to the conversion of potassium phellonate into the copper 

 salt, and not to the removal of cellulose, as had been sup- 

 posed. 



Gilson separated from oak-cork suberic acid (CjTHsoOg) and 

 phloionic acid (CuHaiO^) in addition to phellonic acid. He 

 does not think that these occur as true glycerol esters, since 



* Gilson: "La Cellule," 1890, 6, 63. See also van Wisselingh : 

 " Chem. Zentr.," 1892, 2, 516 ; and Schmidt : " Monatshefte," 1910, 31, 



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