B A K K 



265 



showing the location of the cambium and the different 

 tissues found in the xylem and phloem strands (Fig. 408). 

 It may be thought best to precede this experiment with a 

 similar study of two -year-old stem of moonseed, ivy or 

 other vines. 



430. BARK. In most woody plants that part of the 

 stem which is outside the cambium ring is called bark. 



407. White pine stem 5 years old. The outermost layer is bark. 



At first it contains the epidermis or outer layer of cells, 

 the phloem and the cortex lying between the epidermis and 

 the phloem. The gradual growth of the stem causes the 

 outer dead layers of bark to crack more or less irregularly 

 and finally to split off. Examples of this can be seen on 

 the trunks of any large trees. Before the tree is many 

 years old the cortical cells of the bark become much 

 crushed and are lost to view. The epidermis is shed 

 rather early in the life of the tree. 



