J 34 



PLAN 7' LIFE. 



Hairs of many sorts, jilain, stinging and glandular, and 

 of various sizes, arise from the epidermis (figs. Z^'^—Z^S)- 

 They are essentially like similar structures on the stem (figs. 



113. 114)- 



166. Stomata. — Numerous intercellular spaces bounded 

 by a pair of specialized cells, called guard cells, penetrate 



Fig. 160. 



Fig. 162. 



Fig. 160. — Surface \ lew of epidermis from tlie leaf of oat, shnwing elongated cells (more 

 elongated over vein, ;^ //) and stomata arranged in lines. I^Ioderately magnified. — 

 After Frank. 



Fig. i6r .—Perspective view of a st(jma from the under epidermis of the beet leaf, show- 

 ing the sloping sides of the slit, the crescentic guard cells with cbloroplasts. Higlilv 

 magnified. — After Frank. 



Fig. 162. — Sections through stomata of beet at right angles to their length. Tiie upper 

 figure shows the stoma fipen ; the lower closed. The black line represents the primary 

 wall, to which additional material, especially in the guard cells, has been added. 

 These thickenings serve by their elastitity tn close the stuma. Opening is due to 

 turgor of the guard cells. The cbloroplasts and granular protoplasm are shown. 

 Highly magnified.— After I''rank. 



the epidermis. The whole a])paratus is called a sfoma (si, 

 fig. 159, 160). I'he guard cells are crescentic, sometimes 

 with enlarged ends (fig. 160, like cur\'cd dumb-bells then), 



