248 PHARMACEUTICAL BOTANY 
moderate lobing, seldom to complete subdivision in pinnate or 
tripinnate fashion. Examples: Belladonna, Hyoscyamus, 
Dandelion, Grasses, etc. In microscopic structure, they consist 
of an upper and lower epidermis, the upper epidermis being the 
thicker of the two, the lower epidermis having wavy vertical 
walls. The stomata are wholly or are mainly on the lower 
epidermis. In mesophytic trees and shrubs they are restricted 
generally to the lower surface while in herbs of mesophytes they 
may occur on both surfaces although mostly on the lower surface. 
In mesophytic dicotyledons, the palisade parenchyma is toward 
the upper epidermis and consists of one to three layers of cells. 
The spongy parenchyma is toward the lower and consists of 
irregular, loosely arranged cells with prominent intercellular- 
air-spaces. In a number of mesophytic monocotyledons like 
the grasses and sedges the chlorenchyma is devoid of ore 
cells, being compact and uniform. 
3. DoORSIVENTRAL XEROPHYTIC.—Leaves characterized by a 
thick upper and lower cuticle and by having their numerous, 
small stomata restricted to the lower surface or present more or 
less equally on both surfaces, where they are sunken in depres- 
sions or pits. They may be either firm, leathery, tough, or 
fibrous, or may become swollen up in their mesophyll, chiefly in 
their spongy parenchyma cells, and store considerable mucilage. 
The. object of mucilage is to retain water. Very frequently they 
develop a water-storage tissue above the mesophyll. Their 
palisade tissue is usually well developed, occurring in the cacti 
in many rows. Examples: Boldo, Eriodictyon, Ficus. 
4. DorstvENTRAL Hypropnytic.—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 mesophyll is soft, open, and spongy 
showing large air-spaces. 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 sub- 
merged leaves are modified into bladders which trap insect 
larvee and smaller Crustacez (see Fig. 481). 
