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Related article: 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 (I. ep)\ palisade parenchyma (pal.);
spongy parenchyma (sp. p); xylem (x) Cardizem Cd and phloem (ph) regions of fibrovascular
tissue of stronger vein; long-pointed non-glandular trichome (t); branched tri-
chomes (ft 1 , ft z , ft 3 ); several types of glandular trichomes (gt, gt 2 , gt s , 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
PLANT ORGANS AND ORGANISMS
spaces. The lower epidermis is more or less hairy. Examples:
Dog's Tooth Violet, Asteis.
2. Mesophytic. Leaves tend to subdivision, either to slight or
moderate lobing, seldom to complete subdivision in pinnate or
tripinnate fashion. Example: Dandelion. In microscopic struc-
ture, they consist of an upper and lower epidermis, the upper epider-
FIG. 87. Photomicrograph of cross-section through a portion of the leaf of a
xerophyte, Ficus elastica, showing upper epidermis (u.e.), water storage tissue
(iv.s.), cystolith suspended on stalk within a cystolith sac (cys), palisade paren-
chyma (p.p.), spongy parenchyma (s.p.), vein (v), lower epidermis (I.e.), and
stoma (s). (Highly magnified.) Cardizem Cd
mis being the thicker of the two. The stomata are wholly or are
mainly on the lower epidermis. Hairs are seldom seen. The pali-
sade mesophyll is toward the upper surface, the spongy mesophyll
toward the lower. The intercellular-air-spaces in the spongy paren-
chyma are small.
3. Xerophytic. Leaves characterized by a thick upper and lower
cuticle and by having their numerous, small stomata restricted to
172 PHARMACEUTICAL BOTANY
the lower surface or present more or less equally on Cardizem Cd 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
B. Convergent. In Phormium tenax, Cardizem Cd 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-
Xerophytic. Cardizem Cd 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, Cardizem Cd 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 Sansemera cylin- .
drica, the epidermis shows a tnick cuticle; the stomata are sunken in
cavities of the epidermis; the epidermis and leaf tissue are Cardizem Cd 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
PLANT ORGANS AND ORGANISMS
number. The mesophyll is differentiated into a central spongy paren-
chyme containing bundles, and a zone of palisade cells on either
side facing the epidermises.
Structure and Development of Stomata. Stomata are slit-like
openings in the epidermis of leaves or young green stems surrounded
ep. v. p.p.
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