26 COLLEGE BOTANY 



tkey may be more abundant than the wood fibers. They are 

 the important commercial products in many of our fiber-produc- 

 ing plants, such as hemp and flax, and are used in the manufac- 

 ture of cloth, cordage and many other textiles. 



(2) The wood fibers are very similar to the bast fibers but 

 are usually somewhat shorter. The cell walls are thick and lig- 

 nified. They constitute the woody paxts of the plants and in the 

 dicotyledonous plants are located farther below the surface of 

 the stem than the bast fibers. The quality or character of a wood 

 depends on the specific gravity, hardness, elasticity, strength and 

 other characters of these fibers. They also give strength to the 

 plant. Closely associated with the wood fibers are the tracheary 

 tubes and the tracheids. In fact, they are modified wood fiber 

 cells. The sieve and laticiferous cells are also modified 

 fibrous cells. 



The tracheary tubes (Fig. Y) are formed from fibrous cells 

 by the partial or complete dissolving of the cell walls at the ends 

 of certain long fibrous cells accompanied by a modification of 

 the lateral cell walls, resulting in the formation of long tubes. 

 The modified cell walls are due to peculiar lignin thickenings on 

 the inner surfaces of the walls resulting in the formation of 

 various patterns described as ringj spiral, reticulated, dotted, or 

 pitted tracheary. 



In the ring tracheary tubes the thickenings take the form of 

 rings attached to the inner walls and projecting into the cell 

 cavity; in the spiral tracheary the thickenings are very much 

 like a spiral wire spring just fitting into the tube ; in the reticu- 

 lated tracheary the thickenings form a network on the inner 

 surface of the cell wall ; in the dotted or pitted tracheary the 

 thickenings are such as to leave numerous thin spots or pits. 



