MORPHOLOGY OF HIGHER i'LANTS. 



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 ben'eath it. The two 



- C 



Fig. 106. Stomata and water-pores. A. Transverse section through lower surface 

 of leaf of stramoniu; stoma, v.-ith guard cells (G), containing cytoplasm, nucleus and 

 chloroplastids; K, 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 V'iola 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 l^iola tricolor in 

 surface section. 



contiguous cells are known as guard cells (Fig. 106, G). The 

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

 the cells vary in shape in different plants ; they are more or less elas- 



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