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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