54 



ANCIENT PLANTS 



Principal Types of Plant Cells 



a 



Fig. 21 



EPIDERMAL. 



Epidermis. Protecting layer or skin. 

 Cells with outer wall thickened in 

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

 pare fossil epidermis in fig. 34, e. 



Hairs. Extensions of epidermis cells. 

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

 where e is epidermis and p 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). j, Stomates; 

 e, epidermis cells. Compare fossil 

 Stomates in fig. 8. 



Fig. 23 



