PHARMACEUTICAL BOTANY 
170 
Gross Structure and Histology of Different Types of Dorsoventral 
Leaf Blades.—1. Umbropbytic. —Characterized by leaver mostly 
undivided and having the largest and most continuous leaf expanse. 
Usually the deepest green leaves we have, to enable the leaves to 
Fig. 86.—Transverse section through portion of dorsoventral leaf blade of 
horehound (Marrubium vulgare). Upper epidermis devoid of stomata ( up.ep.); 
lower epidermis which possesses stomata ( l . ep); palisade parenchyma (pal.); 
spongy parenchyma ( sp. p); xylem (*) and phloem (ph) regions of fibrovascular 
tissue of stronger vein; long-pointed non-glandular trichome ( t ); .branched tri- 
chomes (ft 1 , ft 2 , ft 3 )’, several types of glandular trichomes (gt, gt 2 , gt 3 , gl 4 ). 
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 parenchyma having decided intercellular 
