CHAPTER VI. 



THE OAK (CONTINUED) BARK GROWTH OF TREES. 



THE bark in the everyday meaning of the word is that 

 part of the stem external to the cambium. I propose 

 to use the term in this sense in spite of the fact that 

 in English botanical books it is applied only to the 

 tissues external to the cork-cambium. 



The bark increases in thickness in the manner described 

 in the case of wood, namely, by cambium cells, as they 

 develope, assuming the form and nature of phloem. And 

 just as the shells of wood formed by the cambial cylinder 

 are known as secondary xylem, so here the products of 

 cambial activity towards the periphery of the stem are 

 known as secondary phloem. But the growth of the bark 

 is more complex than that of the wood for more than one 

 reason. 



In the first place it is complicated by the existence of 

 the primary cortex. In the young oak stem as in the 

 sunflower the cortex is the region outside the vascular 



