MATERIAL FOR STRENGTHENING PURPOSES 



63 



76. Disposition of material for strengthening purposes. Only 

 two of the many ways in which the stem is strengthened need 

 be mentioned here. In a majority of cases it owes its stiffness 

 mainly to the wood, as shown in Fig. 56. But not infrequently 



FIG. 63 FIG. 64 



FIG. 63. Part of a sieve tube from linden 

 s, sieve plates on the cell wall, x about 900. After Thome 



FIG. 64. Parts of sieve tubes as found in plants of the gourd family 



ss, a sieve plate seen edgewise ; above it a similar one, surface view. Greatly 

 magnified. After Thome 



most of the stiffening material consists of the hard-bast fibers 

 found in the bark. It is this layer in flax (Fig. 60) which is 

 utilized in the manufacture of linen thread and linen fabrics. 



