CH. VI] 



CORK. 



83 



is often described as cork-cambium, but more technically 

 as phellogen. In the same phraseology cork is sometimes 



FIG. 38. 



TRANSVERSE SECTION THROUGH ONE-YEAR-OLD BEECH-BRANCH, 



showing the development of cork. 



c, cuticle. e, epidermis. p, developing cork-layer. 



ph, phellogen. col, collenchymatous cells of the cortex. 



cor, cortex. (The phelloderm is not yet formed.) 



called phellem, and the cortical tissue arising from the 

 phellogen is called phelloderm. The three layers together 

 form the periderm 1 . Thus the bark of the oak comes to 

 be made up of three chief parts ; the original cortex to 

 which on the inside is added secondary phloem arising 

 from the cambium ring, and on the outside the periderm 

 arising from the phellogen. 



The epidermis is stretched and cracked by the cork 

 growing underneath it, and ultimately dies and falls away 

 in flakes. 



1 Some authors use periderm to mean cork only. 



62 



