PLANT ORGANS AND ORGANISMS 
133 
Xerophytic .— Centric laminae are produced gradually by an en- 
croachment of the under on the upper surface, and the swelling of the 
whole. In a completely centric leaf of the succulent kind, like that 
of Sedum, the difference between the upper and lower surface is lost. 
Stomata are found scattered over the entire epidermis. The bundles 
o.r. ep. v p.p. 
are arranged in a circle, the mid-rib being in the center. A great 
deal of mucilage is found stored in the central cells. In a typical 
Xerophytic Centric leaf, like that of the Pine or Sanseviera cylindrica , 
the epidermis shows a thick cuticle; the stomata are sunken in cavi- 
ties of the epidermis; the epidermis and leaf tissue are strengthened 
by scleroid bands in the centric mesophyll. 
ep. p.p. 
Pig. 61. — Photomicrograph of a transverse section of a bifacial leaf of Eucalyp- 
tus globulus showing epidermis (ep.), palisade parenchyma (p.p.), toward both 
surfaces, spongy parenchyma ( s.p .), vein (v), and oil reservoir (o.r.) lined with 
secretory epithelium. (Highly magnified.) 
