5. MORPHOLOGY OF FLOWERING PLANTS
THE STEM
It bears branches, leaves, flowers, fruits, buds (terminal or axillary), nodes and internodes.
Nodes are the regions of the stem where leaves are born. Internodes are the portions between two nodes.
Young stem is generally green and later
often become woody and dark brown.
Functions of stem:
- Spreading out branches bearing leaves, flowers and fruits.
- It conducts water, minerals and photosynthates.
- Food storage, support, protection & vegetative propagation.
Modifications of Stem
- For food storage: E.g. underground stems of potato,
ginger, turmeric, zaminkand, Colocasia etc. They also act as organs of perennation
to tide over conditions unfavourable for growth.
- Stem tendrils: Slender and spirally coiled structures formed from axillary buds. They help plants to climb. E.g. Gourds (cucumber, pumpkins, watermelon) & grapevines.
- Thorns: Woody, straight and pointed structures developed from axillary buds. They protect plants from browsing animals. E.g. Citrus, Bougainvillea.
- Phylloclade: It is a green, flattened or fleshy cylindrical stem containing chlorophyll for photosynthesis. Found in some plants of arid regions. E.g. Opuntia (flattened stem), Euphorbia (cylindrical stem).
- Stolon: Slender lateral branch that arises from the base of the main axis and after growing aerially for some time arch downwards to touch the ground. E.g. mint & jasmine.
- Offset: It is a lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots. E.g. aquatic plants like Pistia and Eichhornia.
- Sucker: The lateral branches that originate from the basal underground part of the main stem. It grows horizontally beneath the soil and come out obliquely upward giving rise to leafy shoots. E.g. Banana, Pineapple & Chrysanthemum.
- Underground stems of grass, strawberry etc. spread to new niches. When older parts die, new plants are formed.
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