54 



ANCIENT PLANTS 



Principal Types of Plant Cells 



Epidermal. 



Epidermis. — Protecting layer or skin. 

 Cells with outer wall thickened in 

 many cases (fig. 21, a and b). Com- 

 pare fossil epidermis in fig. 34, e. 



Fig. 21 



Hairs. — Extensions of epidermis cells. 

 Single cells, or complex, as fig. 22, h, 

 where e is epidermis and / paren- 

 chyma. Compare fossil hairs in figs., 

 79 and 120. 



Fig. 22 



Stomates. — Breathing pores in the epider- 

 mis. Seen in surface view as two- 

 lipped structures (fig. 23). s, Stomates; 

 e, epidermis cells. Compare fossil 

 stomates in fig. 8. 



Fig. 23 



