PRACTICAL WORK. NO. VI. 211 



cork cambium or phellogen, for the structure of which see 

 below ; 



g. phelloderm ; oval, fairly thick-walled cells next 

 below the phellogen, and next to the primary cortex. 



ii. Cut longitudinal radial sections of the same 

 material. Identify the above tissues; the phloem fibres 

 now appear as white thick-walled elements occurring in 

 strands runniog between groups of soft phloem. Cubi- 

 cal crystals arranged in longitudinal rows are very 

 numerous bordering the groups of fibres ; notice too the 

 cluster-crystals mentioned above. Scattered groups of 

 thick- walled pitted cells sclerenchyma also occur. 



iii. Examine a twig of the Hedge Maple (Acer cam- 

 pestre). In the lower, and older, part notice the furrows 

 in the cork due to the cracking caused by growth. 

 Proceeding towards the apex these furrows become less 

 obvious until in the younger part they disappear. 



A transverse section at the younger part should be 

 carefully compared with one taken lower down. In your 

 sketch of the younger part shew, proceeding inwards, 



a. the epidermis ; 



6. cork ; 



c. the phellogen. 



Sketch the larger section to shew the furrows in the 

 cork. 



iv. In a transverse section of a young Beech stem 

 examine carefully the phellogen. Note that the superficial 

 layer of the cortical cells begins to divide, producing a 

 cork cell towards the outside while the inner cell continues 

 to divide, thus constituting the phellogen or cork cambium 



142 



