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PART II. VEGETABLE HISTOLOGY. 



each other, leaving a small opening between them. Each cell 

 of the stoma is called a guard-cell. See Figs. 407 and 408. 



.....a 



Fig. 407. 



FlG. 405. — Portion of lower epidermis of leaf of Gentiana alba, showing lobed epider- 

 mal cells and numerous stomata. Magnified about 65 diameters. 



Fig. 406. — Portion of upper epidermis of leaf of Sanseviera. a, one of the stomata. 

 Magnified about 100 diameters. 



Fig. 407. — Small portion of epidermis of Tulip leaf, showing one of the stomata and 

 portions of adjacent epidermal cells, viewed from above. Magnified 480 diameters. 



Stomata are also shown in Figs. 405 and 406. The opening 

 between the cells is increased or diminished by certain external 

 agencies, as light and the quantity of moisture in the air, and 



