278 



A TEXT-BOOK OF BOTAXY. 



The epidermis usually consists of a single layer of cells, but 

 may have additional layers underneath forming the hypodermis, 

 as in the upper surface of the leaves of species of Ficus (Fig. 113) ; 



Fig. 147. Stomata and water-pores. A. — Transverse section through lower surface 

 of leaf of stramonium: stoma, with guard cells (G), containing cytoplasm, nucleus and 

 chloroplastids; N, surrounding cells; A, intercellular cavity usually filled with cell-sap or 

 watery vapor; E, epidermal cells; M, mesophyll. B. — Surface section of upper surface of 

 leaf of Viola tricolor showing four stomata. C. — Surface section of under surface of leaf of 

 Viola tricolor showing five stomata. D. — A section through the margin of the leaf of Viola 

 tricolor showing a tooth with three water-pores. E. — A water-pore of Viola tricolor in 

 surface section. 



in some instances the hypodermis undergoes a mucilage modifica- 

 tion, as in the leaves of buchu. 



Stomata. — Distributed among the epidermal cells are pairs 

 of crescent-shaped cells known as a stoma, and having an open- 



