Natural vegetative propagation can be defined as when plants grow and develop without human influence.
Natural Vegetative propagation occurs using creeping stems, underground stems and shoots, adventitious buds, bulbils, and root tubers.
Methods of Natural Vegetative propagation
There are different methods plants are naturally propagated without human influence.
Creeping stems
Plants such as sweet potatoes have thin, long, weak stems that creep on the surface of the ground and produce adventitious roots and lateral buds at the nodes.
The horizontal stems are known as runners.
The lateral buds produce new aerial shoots, Often the internodes die off leaving many new plants independent of one another.
When the internodes do not die off, the result is a series of plants linked together by the runners.
Many kinds of grass produce new shoots in this way, for example, the Axonopus compressus.
A stolon resembles a runner except that is situated underground and has internodes that persist for several years.
The lateral buds at the nodes produce aerial shoots and adventitious roots.
Elephant grass (Imperata cylindrica), arrowroot, and passionflower are examples of plants that have stolons.
Both runners and stolons do not store food but conduct it from the parent plants to the new plants.
Some underground stems produce short lateral branches that end in terminal buds.
These lateral branches grow obliquely to the ground level and produce new aerial shoots as well as adventitious roots.
Such lateral branches are known as suckers. Some suckers, such as those of Chrysanthemum, are slender while others, such as those found in bananas, are stout.
Offsets resemble suckers but arise from above the ground level.
They are shorter and thicker than runners and stolons, Certain water plants, for example, water lettuce and water hyacinth, propagate by offsets.
Underground Stems and Shoots
Most underground stems and shoots contain stored food and numerous buds which can grow into new plants at the expense of the stored food.
Rhizomes, corms, and stem tubers are underground shoots.
We shall now study how they serve vegetative propagation.
Rhizomes
At the beginning of the favorable season, the terminal bud is supplied with food from the rhizome and grows into a green aerial shoot.
This soon begins to manufacture food which is sent down to the rhizome for storage.
Some of the manufactured food is sent to lateral buds which grow horizontally into short, stout branches. The rhizome is extended in this way.
The adventitious roots given off from the lower surface of the rhizome keep it at a constant level in the ground.
Finally, when the favorable season ends, the aerial shoot dies down and the rhizome remains dormant underground.
The tissues and buds make use of the stored food. the adventitious roots of the rhizome absorb water from the ground.
The older portion of the rhizome may last for several years but when it finally dies, some separate plants are produced. the ginger plant propagates by rhizomes.
Corms
These are also underground stems that contain stored food for the development of new shoots.
Unlike rhizomes, the direction of growth is vertical.
At the beginning of the favorable season, the terminal bud is supplied with food from the corm and develops into the aerial shoot.
Some of the lateral buds may also receive food from the corm and produce new aerial shoots.
The aerial shoots then begin to manufacture food in their leaves.
This food is sent back, not to the interior of the old corm, but to the particular superficial areas of it to which the shoots are attached.
These superficial areas become swollen with food and develop into new corms.
Meanwhile, the old corm gives up its food and slowly shrivels up.
The corms formed below the lateral shoots are called ‘daughter’ or ‘secondary’ corms.
Each new corm develops adventitious roots at its base.
Some of these have the special function of pulling the corm downwards and so retaining it at the level of the original corm.
These roots are called contractile roots. the outer roots serve for the absorption of water.
When the favorable season ends. the aerial shoots die down. the old lead bases remain as sheathing scale leaves on the surface of the corm.
the portion connecting the new corm with the new daughter corms may die off producing several separate corms.
Unfavorable season, using stored food to sustain their tissues.
Colocasia Amorphophallus and Gladiolus are some parts that propagate by corms.
Stem Tubers
Stem tubers are modified underground stems. they form at the tips of lateral branches.
These grow from axillary buds situated at the lower buried portion of the main stem.
As these branches grow outwards, food accumulates at their tips to form the swollen tubers.
The leaves and axillary buds on the tubers become reduced to form the ‘eyes’ and ‘eyebrows’.
Each one of these axillary ‘buds’ or ‘eyes’ can produce a new aerial shoot that will initially receive a constant supply of food from the tuber.
This shoot soon becomes capable of manufacturing its food.
If a tuber is cut into a few smaller pieces and each piece gives rise to a new aerial shoot.
Adventitious roots do not usually develop from the tuber but the basal buried portion of the main stem,
Bulbs
At the beginning of the favorable season, new adventitious roots develop from the base of the stem and grow into the soil.
The terminal and axillary buds are supplied with food stored in the fleshy leaf bases.
One or more of these buds then proceed to grow above the soil level to produce new aerial shoots.
these aerial shoots eventually manufacture their food which is deposited in the bases of the new leaves, so forming new bulbs.
As the fleshy leaf bases of the original bulb give up their food supply, they are transformed into thin, papery structures. Hence, the new bulbs become enclosed in the protective scaly leaf bases.
New bulbs developing from axillary buds are known as ‘daughter’ or ‘branch’ bulbs.
At the end of the favorable season, the aerial shoots die off, leaving one or more bulbs that lie dormant throughout the unfavorable season.
Adventitious Buds
In plants such as Bryophyllum and Kalanchoe, a series of adventitious buds develop on the leaf.
In the former, each bud develops at the end of a vein at the leaf margin while in the latter, buds develop towards the leaf tip.
In Begonia, a few adventitious buds grow on the surface of the leaf from the veins.
Some buds may also grow from the petiole. In certain cases, for example, in the sweet potato plant, adventitious buds may grow from underground roots. these buds will grow up into new plants.
Bulbils
In some plants, for example, garlic, the lower flowers of the inflorescence are modified into small multicellular structures called bulbils. these detach themselves, fall to the ground and grow into new plants.
In certain plants, for example, yam, small compact bulbils grow in the axils of leaves. in others, groups of bulbils accumulate at the top of the swollen tap roots, for example, Oxalis.
In the Pineapple plant, the sorosis becomes surrounded by a whorl of bulbils at the base as well as at the crown.
Root Tubers
The roots of certain plants, for example, cassava, sweet potato, and dahlia become swollen with food during the favorable season.
These structures do not normally serve for vegetative propagation since most of them do not bear any buds.
However, in certain plants, for example. dahlia and lesser celandine, the swollen fibrous root tubers break away from the parent root system and grow into new plants.
Root tubers of sweet potato bear adventitious buds that can form new shoots, thus enabling the former to serve for vegetative propagation.
