Kinds of Plant Tissues (Cont'd) 



SHAPE, SIZE, AND ARRANGE- 

 MENT OF CELLS 



LOCATION AND 

 FUNCTIONS 



SCLEREN- 

 CHYMA 



Cell walls tough and extremely 

 thickened by cellulose and lignin; 

 walls possess thin areas, known as 

 pits, whose borders or edges are 

 simple and unthickened (unhor- 

 dered pits); protoplasm dies when 

 cell reaches maturity. Two types 

 of sclerenchyma cells: 



(a) Sclerenchyma fibers, which are 

 elongated, pliable, elastic 'cells 

 with pointed ends and great 

 strength. 



(b) Stone cells (sclereids) , which are 

 not elongated but may be irregu- 

 lar in shape, with length and 

 width about equal; minute pit 

 canals extend through thickened 

 walls. 



Provide mechanical support 

 and strength; stone cells 

 abundant in shells of 

 nuts, in gritty masses in 

 fruits (pears), in seed 

 coats, and in bark of 

 trees, etc. ; because of 

 flexibility, strength, and 

 cohesive ability of fibers, 

 some of them are used in 

 making ropes, twine, mats, 

 and other textiles (fibers 

 of flax, hemp, etc. ) . 



6. CORK 



Cell wall contains a waxy, water- 

 proofing material called suberin; 

 cells frequently rectangular and 

 regularly arranged; arise from 

 cork cambium; protoplasm dies 

 soon after cell is formed. 



Forms outer bark of stems 

 and roots of woody plants 

 to give protection against 

 mechanical injury and 

 excessive evaporation; 

 may also be present in 

 other plant structures for 

 same purposes. 



7. XYLEM 



Complex, woody tissues composed of 

 several kinds of cells which are 

 usually elongated and with thick- 

 ened walls. Xylem composed of: 



(a) Tracheids, which are elongated, 

 tapering, single cells with a fairly 

 large lumen (cavity) ; cell walls 

 thickened by spirals or rings of 

 cellulose and lignin and often 

 possess thin areas called bordered 

 pits (edge of pit thickened) ; 

 protoplasm frequently short-lived ; 

 common in cone-bearing trees, 

 etc. 



(b) Tracheal vessels (tubes), which 

 are long, multicellular tuies com- 

 posed of chains of long, cylin- 

 droid cells whose adjacent ends 

 have dissolved and fused; cell 

 walls have thickenings and bor- 

 dered pits as do tracheids. 



(c) Xylem parenchyma which is 

 much like ordinary parenchyma 

 with somewhat thicker walls. 



(d) Xylem (wood) ray cells which 

 are chiefly parenchymatous tissue 

 to conduct materials radially in 

 stems, etc, 



(e) Xylem (wood) fibers which are 

 elongated, fiberlike cells charac- 

 terized by bordered pits. 



Xylem (wood) functions as 

 conducting tissue, trans- ' 

 porting water, mineral 

 salts, etc., upward; thick- 

 ened areas of tracheids, 

 vessels, etc., give strength 

 and support; tracheids 

 common in cone-bearing 

 evergreens; tracheal ves- 

 sels most abundant in 

 higher plants; xylem 

 parenchyma stores foods; 

 ray cells store foods and 

 conduct materials radially 

 across stems, etc. ; xylem 

 fibers give strength and 

 support. 



