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Related article: given form is to be regarded as simple or compound. The number
and arrangement of the parts of a compound leaf correspond with
the mode of venation, and the same descriptive terms are applied
to outline, margin, etc., as in simple leaves.
Leaves are either pinnately or palmately compounded. The term
pinnate is frequently given to the former while that of palmate is
often assigned to the latter. They are said to be abruptly pinnate
or paripinnate when the leaf is terminated by a pair of leaflets; odd
pinnate or imparipinnate when it terminates with a single leaflet.
When the leaflets are alternately large and small, the leaf is inter-
ruptedly pinnate, as the Potato leaf. When the terminal leaflet is
the largest, and the remaining ones diminish in size toward the base
the form is known as lyrate, illustrated in the leaf of the Turnip.
Palmately compound leaves have the leaflets attached to the
1 66 PHARMACEUTICAL BOTANY
apex of the petiole. When these are two in number the leaf is
bifoliate, or binate; if three in number, trifoliate, or ternate, as in
Menyanthes; when four in number, quadrifoliate, etc. If each of
the leaflets of a palmately compound leaf divides into three, the leaf
is called biternate; if this form again divides, a triternate leaf results.
Beyond this point the leaf is known as decompound. In the case
of pinnately-compound leaves, when division progresses so as to
separate what would be a leaflet into two or more, the leaf becomes
bipinnate, as the compound leaves of Acacia Senegal or on the new
wood of Gleditschia; if these become again divided, as in many
Acacia species, the leaf is termed tripinnate. Examples of decom-
pound leaves seen in Cimicifuga and Parsley.
Leaf Texture. Leaves are described as :
Membranous, when thin and pliable, as Coca.
Succulent, when thick and fleshy, as Aloes, and Live Forever.
Coriaceous, when thick and leathery, as Eucalyptus, Uva Ursi
Leaf Color. Petaloid, when of some brilliant color different from
the usual green, as Buy Cardizem Online the Coleus and Begonia, and other plants which
are prized for the beauty of their foliage rather than their blossoms.
Leaf Surface. Any plant surface is :
Glabrous, when perfectly smooth and free from hairs or protuber-
ances. Example: Tulip.
Glaucous, when covered with bloom, as the Cabbage leaf.
Pellucid-punctate, when dotted with oil glands, as the leaves of
the Orange family.
Scabrous leaves have a rough surface with minute, hard points.
Pubescent, covered with short, soft hairs. Example: Strawberry.
Villose, covered Buy Cardizem Online with long and shaggy hairs. Example: Forget- Buy Cardizem Online
Sericious, silky. Example: Buy Cardizem Online Silverleaf.
Hispid, when covered with short, stiff hairs. Example: Borage.
Tomentose, densely pubescent and felt-like, as the Mullein leaf.
Spinose, beset with spines, as in the Thistle.
Rugose, when wrinkled. Example: Sage.
Verrucose, covered with protuberances or warts, as the calyx of
PLANT ORGANS AND ORGANISMS 167
Duration of Leaves. Leaves vary as to their period of duration.
They are: Persistent, or evergreen, if they remain green on the tree
for a year or more.
Deciduous, if unfolding in spring and falling in autumn.
Caducous, or fugacious, if falling early in the season.
Parts of Typical Leaf. The parts of a typical leaf are petiole or
leaf stalk, lamina or blade, and stipules.
Gross Structure and Histology of the Petiole. The petiole in
Monocotyledons is usually a broadened, sheathing basal structure
which connects the lamina to the stem. Into this a set of closed
collateral vascular bundles of the stem extend, these showing xylem
uppermost and phloem beneath; but in the Palmacece, Aracece,
Dioscoreacece and Musacea the petiole in Buy Cardizem Online part or throughout may be
much thickened, strengthened and developed as a semi-cylindric or
cylindric structure frequently showing, as in Palmacea, generally, Buy Cardizem Online
two sets of bundles. In all of these the petiole shows distinct scat-
tered closed collateral bundles embedded in parenchyma and sur-
rounded Buy Cardizem Online by epidermis. In the Monocotyl genus Maranta a special
swelling is found at the apex of the petiole which is termed a pulvinus.
In Dicotyledons the petiole attains its most perfect development
and here usually shows differentiation into a pulvinus or leaf cushion
and stalk portion. The pulvinus Buy Cardizem Online is sensitive to environal stimuli
and in some groups as Oxalidacece and Leguminoscz a gradual increase
in sensitivity up to a perfect response can be traced. Moreover, in
these, if we start with the simpler less sensitive pulvini and pass by
stages to the most complex, we note that a special substance known
as the aggregation body develops in the pulvinar cortex cells and
that this substance undergoes rapid molecular change on stimulation
of the leaf. The stalk portion of the petiole in Dicotyledons is
usually plano-convex or nearly to quite circular in outline; rarely in
certain families does it simulate Monocotyledons in becoming
abruptly or gradually thinned or flattened or widened out so as to
sheath round the stem. The most striking example of this is seen in
the Umbellifera where the flattened sheathing leaf stalk is known as
the peridadium. Such a structure is not peculiar to the Umbelli-
fera for in many Ranunculacece, etc., a similar sheathing development
is observed. The stalk may bear the laminar Buy Cardizem Online tissue on its extremity.
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