252 PHARMACEUTICAL BOTANY 
stoma; in Coca a similar arrangement occurs but the cells are more 
even in size, nevertheless they lack the characteristic papille 
found on the other epidermal cells; in Pilocarpus they are usually 
four in number but quite narrow and more or less crescent- 
shaped; in Uva Ursi their number is usually seven to eight and 
their arrangement radial around the stomatal apparatus. 
ep pal 
Fic. 170.—Photomicrograph of a transverse section of a bifacial leaf of Eucalyp- 
tus globulus showing epidermis (ep), palisade parenchyma (pal), toward both 
surfaces, spongy parenchyma (sp), vein (v), and oil reservoir (o0.r.) lined with 
secretory epithelium. (Highly magnified.) 
On all dorsiventral leaves, the stomata arise more abundantly 4 
on the lower epidermis, less abundantly on the upper. Excep- 
tions to this rule are due to the peculiar readaptation of the leaf to 
its surroundings. Thus, in the reversed types of leaves (twisted 
in a half circle), the stomata, formerly on the lower surface, have 
migrated to the upper surface which now has become the phys- 
iological lower surface. 
