WOODY FIBERS 



oxygen. In addition to stomata some leaves possess groups of water 

 stomata which differ from transpiration stomata in that they always 

 remain open, are circular in outline, give off water in droplets directly, 

 and lie over a quantity of small-celled glandular material which is in 

 connection with one or more fibrovascular bundles. 



Endodermis is the starch 

 sheath layer of cells, constituting 

 the innermost layer of cortex 

 whose radial walls are more or 

 less suberized. 



Cork or suberous tissue is com- 

 posed of cells of tabular shape, 

 whose walls possess suberized 

 layers. Its cells are mostly filled 

 with air containing a yellow or 

 brownish substance. It is derived 

 from the phellogen or cork cam- 

 bium which cuts off cork cells 

 outwardly. Cork tissue is devoid 

 of intercellular air spaces. It is 

 protective in function. 



Laticiferous tissue is to be seen 

 in many groups of plants principal 

 among which are the Asclepia- 

 daceae, Euphorbiacese, Apocynacese 

 Urticaceae and Papaveraceae. Its 

 cells are elongated, tubular, often 

 branched and penetrate all the 

 organs of plants in which they are 

 found. They contain a milky- 

 white or colored emulsion of gum- 

 resins, fat, wax, caoutchouc, and 

 in some cases, alkaloids, tannins, salts ferments, etc. 



Cribifonn or Sieve tissue consists of superimposed, elongated, 

 tubular, thin-walled cells whose transverse walls, called sieve plates, are 

 perforated, permitting of the passage of albuminous substances from 

 one cell to another. 



Woody Fibres are elongated, thick- walled, and taper-ended lignefied 

 elements found in the xylem region of the fibrovascular bundle accom- 



-I, Epidermis of oak leaf; 2, 

 epidermis of Iris leaf, both viewed from 

 the surface; 3, group of cells from petal 

 of Viola tricolor; 4, two epidermal cells in 

 cross-section showing thickened outer wall 

 differentiated into three layers, namely, 

 an outer (Cuticle, cutinized layer (shaded), 

 and an inner cellulose layer; s ^nd 6, 

 epidermal outgrowths in the form of 

 scales and hairs. (3 after Strasburger, 4 

 after Sachs, and 5 after de Bary.) 



