XVI 



FIBER CROPS 



CLASSIFICATION AND PRODUCTION 



391. Materials for Fibers. There are two sources of fibers: 

 animal fibers, of which there are two kinds, wool and silk, and 

 vegetable fibers. 



The cells of plants are divided into two kinds : ( I ) cells 

 with soft walls, having but little structural or tensile strength, 

 easily subject to decay and usually more or less globular in 

 shape, known under the general term of parenchyma tissue. 

 Young plants and the young parts of plants consist largely of 

 these soft cells of parenchyma tissue. It is for this reason that 

 the young parts of plants collapse or wilt when water is with- 

 drawn from the cells. (2) Cells with thickened and tough 

 walls. Such cells are known as wood cells and constitute the 

 bulk of what is known as wood. The wood cells are of two 

 kinds: (a) ducts or vessels consisting of cells placed end' to 

 end with the partitions removed, thus constituting continuous 

 passage through the plant and (b) wood cells or fibers, which 

 are elongated more or less spindle-shaped cells with pointed 

 ends. These cells overlap each other, and usually occur in a 

 continuous bundle of cells, known as fibrovascular bundles. In 

 the softer parts of all higher plants and throughout the stems 

 and leaves of endogenous or monocotyledonous plants, these 

 fibrovascular bundles occur at more or less irregular intervals, 

 while in exogenous or dicotyledonous plants, the hard parts 

 consist almost exclusively of wood ducts and fibrovascular bun- 

 dles. 



