Aerial stems The structure that holds the leaf called
petiole.
These modified aerial stems perform unusual The green expanded part of the leaf is
functions. Different forms of these stems are called lamina or leaf blade.
the following
Venation
Stem tendril : e.g. Passiflora
The arrangement of veins and the veinlets in
Stem thorn : e.g. Duranta the lamina of leaf is termed as venation.
Pylloclade : e.g. Opuntia Veinlets form a network – reticulate venation.
(dicot leaf)
Cladode : e.g. Asparagus
Vein runs parallel to each other – parallel
Bulbil : e.g. Dioscorea
venation. (monocot leaf)
Modifications of Stem
1. For food storage: Rhizome (ginger),
Tuber (potato), Bulb (onion), Corm and
Colocasia).
2. For support: Stem tendrils of
watermelon, grapevine, and cucumber.
3. For protection: Axillary buds of stem of Types of leaf
citrus, Bougainvillea get modified into
pointed thorns. They protect the plants 1. Simple Leaf : when the lamina is entire or
from animals. when incised, the incisions do not touch
4. For vegetative propagation: the midrib.
Underground stems of grass, strawberry, 2. Compound Leaf : When the incisions of
lateral branches of mint and jasmine. the lamina reach up to the midrib breaking
5. For assimilation of food: Flattened stem it into a number of leaflets
of opuntia contains chlorophyll and
performs photosynthesis. Bud present in the axil of petiole in both
simple and compound leaf.
LEAF
Bud never present in the axil of the leaflets of
Developed from shoot apical meristem, compound leaf.
flattened, green structure.
Manufacture the food by photosynthesis. It Pinnately compound leaf: number of leaflets
has bud in axil. present in a common axis called rachis, which
represents the midrib of leaf.
A typical leaf has leaf base, petiole and
lamina. Palmately compound leaves: leaflets are
Leaf attached to the stem by leaf base. attached to the common point i.e. at the top of
May bear two small leaves like structure the petiole.
called stipules.
Leaf base may swollen to form pulvinus.
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