12 FAMILIAR TREES 



autumn, are not uncommon objects in hedgerows 

 or copses. The whole plant is remarkable for its 

 smoothness, for even when the young green wood 

 becomes grey from the development of cork beneath 

 the epidermis, the bark retains an even surface. A 

 point of some physiological interest occurs in connec- 

 tion with this formation of cork. A few woody plants, 

 such as Mistletoe and the Pennsylvanian Maple (Acer 

 Pennsylva'nicwm L.), never form any cork at all, but 

 retain their epidermis and their green colour. Others, 

 such as the Willows and the Poma'cece~ (i.e. Apples, 

 Pears, etc.), form cork from the epidermis itself, and, 

 like most trees, do so towards the end of the first 

 summer in the life of the shoot. The majority of 

 trees form their cork a little below the epidermis, so 

 as to bury the green layers of the bark beneath its 

 opaque tissues, whilst both epidermis and cork are 

 subsequently split into longitudinal cracks, which 

 may widen into the deep furrows so familiar in the 

 bark on the trunks of Oaks, Elms, or Poplars. 

 Anyone cutting a switch of Hazel, Holly, Privet, or. 

 in fact, almost any wood, may notice the bright green 

 layer beneath the dull-coloured external cork. In 

 some few plants, such as the Clematis, the Vine, and 

 the Honeysuckle, cork originates yet deeper, viz. in 

 the "bast," or inner layer of the bark, which, as a 

 consequence, conies away in long strips ; but in 

 Evxtnymus, whilst it arises, as in the majority of 

 trees, just below the epidermis, its formation takes 

 place not on yearling shoots, but on those several 

 years old ; and until it is formed the branch remains 

 green externally. 



