Leaves - 1
Leaves are best known as the photosynthetic organs of plants, and much of the
leaf "architecture" reflects this function.
Leaves are part of the plant's shoot
system, attached to stems at nodes.
The regions along the stem between leaves
Leaves exhibit far more variation in shape (morphology) than do
stems and roots.
Leaf shape, size, venation pattern, margins, tips and bases are
all used in identification of plant species (with appropriate vocabulary).
Most leaves, however, have two common features: the blade (or lamina), the
flattened portion of the leaf, and the petiole, or leaf stalk, which attaches the
leaf to the stem.
Leaves that do not have a petiole are sessile, and often sheath
the stem at the base of the leaf.
Stipules, small leaf-like growths near the base
of the petiole, may or may not be present.
Buds are located in the axil of a leaf
with the stem.
Leaf morphology varies in monocots and eudicots, too, with monocots generally
having linear leaves that sheath the stem at the base and eudicots having almost
any shape, but typically with a petiole.
Leaves have a vascular connection to the stem through the petiole. Vascular
tissue in leaves comprises the veins.
In early development, a procambium strand
from the shoot meristem branches out into each leaf primordium.
This is the leaf
Similar strands of procambium branch out into buds, the bud traces.
They leave a procambium gap in the stem tissue called the leaf trace gap and bud
The traces and gaps can often be seen in the shoot meristem.
Leaf venation patterns are also an important distinction between monocots and
Monocots usually have parallel veins; eudicots have netted veins,
generally with a significant midvein.
Eudicot leaves may have pinnate venation
(with veins branching regularly from the midvein) or palmate venation (with major
veins radiating from the leaf base).
tree, which is a gymnosperm, has
leaves with dichotomous venation.
It is unique.