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PHARMACEUTICAL BOTANY 
the lower surface or present more or less equally on both surfaces, 
where they are sunken in depressions. They may be either firm, 
leathery, tough, fibrous, or may become swollen up in their meso- 
phyll chiefly in their spongy parenchyme cells and store consider¬ 
able mucilage. Examples: Yucca, Ficus, Aloe, Agave. Succulent 
forms like Aloe generally possess a thin but tenacious cuticle. 
4. Hydrophytic.—All gradations are seen. In pond plants, such 
as the Water Lily, the leaves have long split petioles which bring 
the blade up to the surface of the water. The stomata are entirely 
on the upper surface. In Ranunculus, the lower leaves are cut up 
into filiform segments. These are devoid of stomata. Their meso- 
phyll is soft, open, and spongy. The epidermis is quite thin. The 
upper leaves are floating, trilobed, and have stomata only on their 
upper surface. In Utricularia, some of the filiform submerged leaves 
are modified into bladders which trap insect larvae and smaller 
Crustaceae. 
B. Convergent.—In Phormium tenax, the base of the blade is 
sheathing, it then converges and opens out above. In the various 
species of Iris the petiole is sheathing, the upper part being fused 
(mostly seen in monocotyls). 
C. Centric.— Succulent — Nearly always associated with Xero- 
phytes.;. 
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 
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 cylin- 
drica, the epidermis shows a thick cuticle; the stomata are sunken in 
cavities of the epidermis; the epidermis and leaf tissue are strength¬ 
ened by scleroid bands in the centric mesophyll. 
D. Bifacial.—Leaves with laminae which stand edge on in relation 
to the sun’s rays. The best illustrations are seen among dicotyle¬ 
dons, such as Eucalyptus, Callistemnon, and other genera of Myr- 
tacece. Both surfaces are similar, having stomata about equal in 
