i3° 
PHARMACEUTICAL BOTANY 
other trees and shrubs of the Legume family, the stipules become 
modified for defensive purposes as spines or prickles. In the Sarsa- 
parilla-yielding plants and other species of the genus Smilax they 
undergo modification into tendrils which are useful in climbing. 
The Lamina. — This as was previously indicated represents an ex- 
pansion of the tissues of the petiole, but in sessile leaves is directly 
attached to the stem and so a direct stem outgrowth. 
Mode of Development of the Lamina of Leaves. — The lamina of 
leaves develops in one of six ways. 
1. Normal or Dorsoventral. 
2. Convergent. 
3. Centric. 
4. Bifacial. 
5. Reversed. 
6. Ob-dorsi-ventral. 
The first four will be considered. 
A. Dorsoventral (the commonest). 
(a) Dorsoventral Umbrophytic.- — Flattened from above downward. 
Plants with such leafblades tend to grow in the shade. 
(b) Dorsoventral Meso phytic. — Similar to the former, but plants 
usually grow directly in the open and exposed to sunlight and winds. 
(c) Dorsoventral Xerophytic. — Similar to former, but plants not 
only grow exposed, but exposed to hot desert conditions or to cold 
vigorous conditions. 
(, d ) Dorsoventral Hydro phytic. — All transitions between typiaal 
mesophytic forms to those of marshy places, to swamps and borders 
of streams and finally with leaves wholly emersed, the last a com- 
pletely hydrophytic type. 
Gross Structure and Histology of Different Types of Dorsoventral 
Leaf Blades. — 1. Umbrophytic. — Characterized by leaves mostly 
undivided and having the largest and most continuous leaf expanse. 
Usually the deepest green leaves we have, to enable the leaves to 
absorb scattered and reduced rays that pass in through high trees 
and shrub overhead. Their texture is usually thin and soft. In 
microscopic structure they are covered with a cutinized epidermis 
which has all the stomata on the lower surface. The mesophyll is 
fairly spongy, the spongy parenchyme having decided intercellular 
