94 



BOTANY FOR BEGINNERS 



CHAP. 



spoken of as forming a tissue. In the higher plants there are 

 three kinds of tissue systems, they are called epidermal 

 tissue, vascular tissue, and ground tissue. The above 

 tissues may be primary or secondary. Primary tissues are 

 formed from the growing cells of the embryo, and the secondary 

 tissues from those new layers of growing cells which are formed 

 from the embryonic cells. 



EPIDERMAL TISSUE 



Epidermal Tissue. Those cells which cover the plant 

 and protect the deeper parts from injury, form the epidermis. 



FIG. 122. Surface view of the epidermis from FIG. 123. Surface view of the 

 underside of leaf of Balsam, showing stomata. epidermis of the Dog's 



(X 160.) (S.) Mercury. (X 300.) (S.) 



As a rule the epidermis is only one cell in thickness, and the 

 cells do not contain any chlorophyll. The protoplasm of the 

 epidermal cells is reduced to a very thin layer which lines the 

 cell-walls, and the cavities of the cells contain a colourless cell- 

 sap. The outer wall of the epidermal cells forms a cuticle, which 

 protects the deeper tissue from a too rapid loss of water. 



Stomata are found in the epidermis of all those parts of 

 plants which are exposed to the air. Each stoma is a minute 

 opening between two cells which contain chlorophyll and are 

 called guard-cells. The stoma is formed by a young epider- 

 mal cell becoming divided by a septum into two equal cells. 



