136 



CORK 



a continuous tissue consisting of numerous radial files of cells, 

 each file (Fig. 65, 1-6) representing the product of one cork- 

 cambium cell. This tissue is the cork and, apart from the 

 absence of intercellular spaces between its cells, it is especially 

 characterised by a chemical modification of the cell-walls spoken 

 of as suberisation. This latter renders them practically imper- 

 vious alike to gases and to liquids, features to which cork owes 

 its utilisation in closing bottles. 



PH. 



c.c. 



Ctt. 



FIG. 65. Transverse section through the cork layer in the stem of the 

 Elder (Sambucus). c.c., cork-cambium ; cu., cuticle ; ep., epidermis ; 

 Ph., phelloderm ; 1-6, successive segments of the cork in order of 

 production. 



Suberisation is known to be due to the presence of various 

 fatty compounds, and hence the walls of the cork are coloured 

 by the same reagents (Scharlach red, etc.) as are employed for 

 staining fats. A yellow-brown colouration is assumed with chlor- 

 zinc-iodide, and a yellow one with strong potash. A marked 

 green colouration is obtained by treating cork-cells with a freshly 

 prepared alcoholic solution of chlorophyll, which is allowed to 

 act for about a quarter of an hour in the dark. On boiling with 

 concentrated potash, large yellow globules often escape from the 



