88 THE ELEMENTS OF VEGETABLE HISTOLOGY 

 EPIDERMAL TISSUES 



Epidermal tissues occur on the exposed surfaces 

 of all plant organs and parts other than those of woody 

 structure. Thus leaves, green stems, fruits, seeds 

 and floral parts possess this covering tissue classed 

 as epidermis. The epidermal tissues are derived 

 from the outermost layer of the dermatogen region, 

 and the cell walls are more or less thickened by depo- 

 sition of cutin, in or around, the original cellulose 

 wall. Cutinized cell walls are practically waterproof. 

 Silicates and other inorganic materials are often pres- 

 ent in the epidermal tissues of grasses, and probably 

 aid in the support of those plants in which poor develop- 

 ment of fibrous supporting tissues is noteworthy. 

 Cutinized tissues frequently have the power of secret- 

 ing or producing waxes and resins. The gloss on the 

 surfaces of certain leaves is due to the presence of 

 a waxy material which serves as an additional pro- 

 tection against access of water through the epidermis. 

 Resins and sticky substances, occasionally present 

 on the surfaces of leaves and stems, serve the purpose 

 of preventing insect attacks and keeping ants or other 

 crawling insects from gaining access to the flowers. 

 Many of the resins are strong antiseptics and will 

 prevent infection of plant tissues. 



Membranous Epidermal Tissues. — The epidermal 

 tissue covering leaves, green stems, floral organs and 

 several classes of fruits is in the form of a thin layer 

 of cells. The epidermal membrane of leaves and 

 green stems is colorless and transparent, while that 

 covering fruits and floral parts is usually colored by 

 deposition of various cell contents and is therefore 



