THE STRUCTURE OF STEMS. 



219 



consisting of peculiar cells, called fiast-cetts, of re- 

 markable length and flexibility, and having very 

 thick walls (Fig. 392). They usually form layers 

 like the leaves of a book, and hence this portion of 

 the bark is called the liber. The length and tough- 

 ness of its fibres have led to its use in 

 thread, cord, and cloth. The bundles 

 of bast-cells are always vertical, and are 

 separated by medullary rays, which 

 correspond to those of the woody sys- 

 tem inside the cambium. 



FIG. 392. 



FIG. 398. 



I 



Fibres of the liber, or bast-cells, and 

 woody fibres from the linden, or bass- 

 wood, are shown in Fig. 393 (Gray), a 

 is a bast-cell, from the bark of Ameri- 

 can basswood, while 5 is woody tissue, 

 from the same tree, showing the upper 

 end of a spirally-marked vessel ; c is a separate cell 

 of the wood. They are all equally magnified. 



Besides the immensely greater length of the bast- 

 cells, they have also very much thicker walls than the 



