THE BARK. 



25 



Section 2. — The Bark. 



45. The bark lies immediately beneath the epidermis. It 

 consists of several layers. In the early state it is entirely cel- 

 lular, and is exactly like the pith with which it is in contact ; 

 but by the production of vessels and woody fiber, they are sepa- 

 rated and become very different in appearance and constitution. 

 The bark consists of two portions, the cellular and vascular, 

 the latter of which is called liber, and is the inner portion of 

 the bark. The cellular portion is usually divided into two por- 

 tions. The outer portion is called the suberose or corky layer, 

 or Epiphlceum, Fig. 22 ep. It is composed of cubical or flat- 

 Fig. 22. 



p — the pith ; m — medullary sheath ; w w w — woody fiber ; 

 dad — dotted ducts ; c — eambrim ; /—liber; re — mesophloe- 

 um ; ep — epiphlceum ; e— epidermis ; mr— medullary rays. 



tened cells, having no coloring matter within them, but turning 

 brown by age. It is sometimes composed of a single layer of 

 cells, at others it is produced in great quantities, as in the Cork- 

 tree. The form of the cells makes it easy to distinguish it from 

 the subjacent layer. 



The inner cellular layer of the bark is called the mesophloeum, 

 Fig. 22 ce. It consists of prismatic cells, usually inclosing the 

 green coloring matter that gives color to the young stem. It 

 lies looser than the suberose layer, and is largely developed in 

 the conifer oe. The lactiferous tissue is found beneath this layer. 



46. The epidermis, cellular integument, and liber, may be 



45. Of what does the bark consist? Into how many portions is the cel- 

 lular divided ? Describe the suberose layer. What is the inner cellular 

 layer called ? Describe it. — 4G. Where may the several parte of the bark be 

 seen I How often are they formed i 





