SUPPORTING TISSUES 105 



Fibrous Tissues. — Fibrous tissues are found in 

 practically all parts of the plant excepting the seed, 

 although the relative amount present in the different 

 organs varies considerably. The greatest amount is 

 found in woody stems and the least in floral organs. 

 Each fiber is an elongated or spindle-shaped cell and 

 is always several times longer than it is broad. The 

 ends of these fiber cells may be sharp-pointed or blunt, 

 with oblique end walls. Occasionally the walls retain 

 part of the original cellulose around which the lignin has 

 been deposited, and this combination is termed ligno- 

 cellulose. The protoplasmic contents are usually lack- 

 ing in fiber cells, and in well-matured plants the fibers 

 are to all intents dead tissue. The fiber-cell walls 

 are usually more or less thickened through the ligni- 

 fication process and in some instances appear striated, 

 or show fine markings extending parallel to the length 

 of the fiber. The cell cavity is termed the lumen of 

 the fiber and may be of large or small size, depending 

 upon the thickness of the wall. Certain fiber cells 

 show pores or small openings in the wall of the cell 

 through which materials may pass from the intercellular 

 space into the lumen. In comparatively few instances 

 the fibers are branched and, instead of appearing as 

 long tapering cells, are irregular in form. Non-proto- 

 plasmic contents or cell inclusions occasionally occur 

 in the lumen of a fiber, and may include calcium 

 oxalate crystals, starch and coloring materials. Fibers 

 containing calcium oxalate crystals within the lumen 

 or apparently upon the surface of the fiber are termed 

 crystal-bearing. In descriptions and illustrations of 

 fiber cells the longitudinal or side view is usually con- 

 sidered, as on sectional view one merely obtains an 



