MORPHOLOGY OF HIGHER PLANTS. 



193 



Stomata. — Distributed among the epidermal cells are pairs 

 of crescent-shaped cells having an opening between them, known 

 as a pore or stoma, which leads to a cavity beneath it. The two 



Fig. 106. 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 le^f 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. 



contiguous cells are known as guard cells (Fig. 106,' G). ^he 

 adjoining walls of the guard cells are alike in transverse section, but 

 the cells vary in shape in diflferent plants ; they are more or lesS efas'- 



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