CHAPTER VII. 



BARK. 



Bark in Euonymus and Beech Superficial periderm Bark of the 

 Birch Ring- bark Scaly bark of Plane and Sycamore Scaly 

 bark of Scots Pine Fissured bark Tow-like peeling of bark 

 Hardness of bark Soft bark Stone-bark Protective functions 

 of bark Thick bark of light-demanding trees Thin bark 

 Injury from sunlight and frost. 



WE have seen, from our study of the shoots and twigs 

 (Volume I), that the tegumentary system gradually under- 

 goes changes which result, in most cases, in the replace- 

 ment of the epidermis by cork, or periderm-layers, and 

 that when these layers, which are impervious to water, 

 develope deep down in the cortical tissues of a branch or 

 stem, all the tissues outside the water-tight layers of cork, 

 die off and constitute Bark. 



There are, moreover, other characters of bark using 

 the word in this wider and looser sense which are due to 

 the place of origin of the periderm and the mode of its 

 action in cutting out the true bark, as described above. 



In Euonymus, for instance, and even in the Beech in 

 certain cases of very old stems, the deeper cork-layers are 

 formed irregularly, in spots as it were, in the cortex, 

 resulting in the development of isolated scattered patches 



