Page 8 - Lesson Notes-Morphologyof flowering plant

axiallary buds, e.g., Passiflora (passion flower).
(b) Extra axillary Develop near the axillary bud, e.g., Lujfa, Cucurbita (pumpkin), etc.
(c) Apical bud These are modified to form tendrils, e.g., Vitis vinifera.
(d) Floral bud These are modified to form tendrils, e.g., Antigonon.
Stem Thorns
The stem thorns are stiff, woody, sharp and pointed. They develop from axillary bud.
They protect the plants from browsing animals, e.g., Citrus, Duranta, Bougainvillea,
Pomegranate, etc.
Prickles
These are modified stems and act as climbing organs. They protect the plants from
grazing animals and also help in climbing in some cases, e.g., Argemone maxicana
(prickly poppy), Rosa indica (rose), Bombax (sembal), etc.
Phylloclade
These are green, flattened structures bearing several nodes and internodes. The true
leaves are reduced to spines or scales. They show unlimited growth. Some
phylloclades also store food and water. The phylloclades are examples of some
xerophytic plants, e.g., Opuntia (nagaphani), Casuarina, Euphorbia.
Cladodes (Cladophylls) .
They are green photosynthetic stems generally one inter node long. These develop
by the modification of only stem branches of limited growth and are green
(photosynthetic). The true leaves of the plant are reduced to scales or spines, e.g.,
Ruscus, Asparagus.
ii. Bulbils
These are modified vegetative or floral buds arising in the axil of scale or foliage
leaves. The bulbil helps in vegetative propagation, e.g., Lilium, Agave, Dioscorea (wild
yam), Oxalis, etc.
The Leaf
The leaf is a lateral, generally Battened structure borne on the stem. It develops at
the node and bears a bud in its axil. The axillary bud later develops into a branch.
Leaves originate from shoot apical meristems and are arranged in an acropetal
order. They are the most important vegetative organs for photosynthesis.
Parts of a Leaf
The leaves also consist of two lateral outgrowths called stipules at their bases.
A typical leaf has three main parts.
i.Leaf Base (Hypopodium)
The leaf is attached to the stem by the leaf base. Monocots, the leaf base is said to
be sheathing as it expands and partially and wholly surrounds the stem. In dicots, the
leaf base bears two lateral outgrowths called stipules.
In some leguminous plants, the leaf base may become swollen which is called the
pulvinus. Leaves with stipules are called stipulate and those without them are
termed as exstipulate.
ii. Petiole (Mesopodium)
It is the stalk of a leaf. Petiole help hold the leaf blade towards light. Petiole raises
the lamina high to the level of stem so as to provide maximum required exposure to
light and air.
iii. Lamina (Epipodium)
The lamina or leaf blade is the green, expanded part of the leaf with veins and
veinlets. It has a prominent median vein called the midrib. It produces thinner lateral