MODIFICATION OF PLANT PARTS
Modified Roots: Specialized functions of varied nature are performed by the modified roots which adapt themselves according to the particular need of the plant. The following are a few such types.
MODIFIED TAP ROOT: (For storage of food)
A) Fusiform Root: When tap root is swollen in the middle and gradually tapering towards the apex and the base being more or less spindle-shaped in appearance. Example: Radish.
B) Napiform Root: When the root is considerably swollen at the upper end becoming almost spherical and sharply tapering at the lower part, it is said to be napiform. Example: Turnip and beet root.
C) Conical Root: When the root is broad at the base and it gradually tapers towards the apex like a cone, it is said to be conical. Example: Carrot.
D) Tuberous Roots: When the root is thick and fleshy but does not maintain any particular shape, it is said to be tuberous or tubercular as in four o’clock plant.
MODIFIED ADVENTITIOUS ROOTS
A) Tuberous Root: This is a swollen root with out any definite shape as in sweet potato.
B) Fasciculate Root: When several tuberous roots occur in a cluster at the base of stem they are called fasciculate as in dahlia.
C) Nodulose Root: When the slender root becomes suddenly swollen at or near the apex it is said to be nodulose; example: turmeric.
D) Beaded Root: When there are some swellings in the root at frequent intervals it is said to be beaded root as in Indian spinach and in some grasses.
E) Annulated Root: When the root has series of ring like swellings on its body it is said to be annulated.
F) Stilt Root: When roots arise from the first few nodes of the stem and penetrate obliquely down in to the soil and give support to the plant; example: maize, sugarcane.
G) Prop Roots: They give mechanical support to the aerial branches. The lateral branches grow vertically downward into the soil and acts as pillars; example: banyan.
H) Climbing Roots: Roots produced at the nodes and often from internodes especially in climbing plants like piper & hoya. Plants attach themselves to their support and climb it using these roots.
I) Respiratory Roots: In some aquatic plants the floating branches develop a special kind of adventitious roots which are soft, light, spongy and colorless. They usually develop above the surface of the water and serve to store up air, thus they facilitate respiration and are called respiratory roots.
J) Epiphytic roots: There are certain plants, commonly orchids, which grow on branches of trees. Such plants are known as epiphytes they are not parasitic in nature. They develop special kind of aerial roots which hang freely in the air and absorb moisture from the surrounding air.
K) Assimilatory Roots: Branches of tinospora climbing on neighboring trees produce long, slender, hanging roots which develop chlorophyll and turn green in color. They carry on carbon assimilation.
MODIFIED STEMS
Stems of certain plants develop underground and often look like roots. They have nodes and internodes, scale leaves and bud on them. These are of different types as:
Rhizome: The rhizome is a thickened, prostrate, underground stem provided with the distinct nodes and internodes, scaly leaves at the nodes. It may be branched or un-branched. Example: canna, ginger, turmeric, water lily, etc.
Tuber: This is a swollen end of a special underground branch. E.g., Potato (Solanum tuberosum). It has on its surface a number of eyes or buds which grow up into new plants.
Bulb: This is another underground modified shoot consisting of a shortened convex or conical stem, a terminal bud and numerous scale leaves with cluster of fibrous roots at the base. The inner scales of the bulb are usually fleshy storing water & food. The terminal bud grow into the aerial shoot common examples are onion, garlic, tuberose & most lilies.
Corm: This is a condensed form of rhizome and consists of a stout, solid, fleshy underground stem growing in the vertical direction. It is more or less rounded in shape or often somewhat flattened from top & bottom. It bears one or more buds in the axils of leaves and some of these buds grow up into develop from the base. E.g., gladiolus & saffron (crocus).
SUB-AERIAL MODIFICATIONS OF STEM (For vegetative propagation)
Some of the lower buds of the stem in certain plants grow out into long or short, slender or stout lateral branches these are as follows:
A) Runners: Oxalis, dog grass.
B) Stolon: Strawberry & chlorophytum etc.
C) Offset: Water lettuce, Water hyacinth.
D) Suckers: Banana, pineapple and chrysanthemum.
AERIAL MODIFICATIONS OF STEM
Vegetative and floral buds which would normally develop into branches & flowers often undergo an extreme degree of modification for definite purpose:
A) Stem tendrils: For climbing, like most of the climbing plants.
B) Thorns: For protection. E.g., Rose, acacias, jujube etc.
C) Bulbils: For vegetative reproduction. E.g., Agaves.
MODIFICATION OF LEAVES
Leaves of many plants which have to perform specialized functions become modified into distinct forms.
- Leaf tendrils: Tendrils are slender, spirally coiled spring like structures. They are highly sensitive to contact and when they come in contact with any support, tendrils coil around the support like the stem twines. In glory lily (Gloriosa superba) the leaf apex is modified into a tendril. In pea (Pisum sativum) the terminal leaflets of a uni-pinnately compound leaf are modified into tendrils.
- Pitchers: Example pitcher plant.
- Scale Leaves: In many desert plants, the leaves are highly reduced and appear as scales. The scale leaves are thin, membranous, dry, stalk less and brownish or colorless. In plants where the leaves are reduced to scales in order to minimize transpiration, the function of photosynthesis is relegated to the stems (cladodes).
- Leaf Spines: In some plants, leaves or parts of leaves may be modified into spines. In Opuntia (prickly pear) leaves are poorly developed and fall of very early, but the minute leaves of the axillary bud are modified into spines. The spines act as defensive structures.