STRUCTURE AND ARRANGEMENT OF STOMATA 



47 



in the direction perpendicular to the surface. This straightens some- 

 what the walls that bulge out to form the aperture and so opens up 

 the stoma. As the cells dry out the turgidity decreases, the cells 

 collapse somewhat, and the walls that form the aperture come nearly 

 or quite together, thus closing the stoma and greatly reducing the 

 amount of water that may be given off by transpiration. 



Fig. 18.— Stomata. A, B, from Solanum tvberosimt, in face view and cross- 

 section; C, from Pyrus mains; I), E, from Laduca saliva; F, from Medeola 

 virginica; G, from Apleclrum. hyemale; H, from Polygonalvrn hiflorum; I, J, K, 

 from Zea Mays: I, face view; /, cross-section through end of stoma; K, median 

 cross-section; L, from Cuciimis salivus {F, G, H, and J, after Copeland). (From 

 Fames and McDaniels— Introduction to Plant Anatomy, New York, McGraw- 

 Hill Book Company, Inc.) 



