Shoot system
It is a plant’s aerial, the green, ascending organ that develops from the embryo’s Plumule. In nature, it is positively phototropic. It is made up of stems, leaves, and flowers.
The Shoot system’s characters
1. The shoot system is a plant body’s aerial, ascending organ that develops from an embryo’s plumule.
2. It is Phototropically positive and geotropically negative.
3. It is made up of a central, cylindrical axis known as ‘Stem.’
4. The Stem is made up of different nodes, with an ‘Internode’ zone between them.
5. A-flat, green, lateral appendage known as a ‘Leaf’ grows at each node.
6. Terminal bud’ is located at the stem’s tip.
Types of stems:
There are two types of stems.
They are 1. Erect Stem. 2. Weak stem.
Erect Stem:
‘Erect stem’ refers to an aerial stem that stands upright without any support. It consists of the following types:
A) Herbs: ‘Herbs’ are little plants with soft, succulent, green, and less branching stems. Example, Sunflower, and paddy.
B) Shrubs: Shrubs are medium-sized plants with a hard, woody stem that is branched and has a bushy appearance.Example Hibiscus, and Custard apple.
C) Trees: ‘Trees’ are huge, tall plants with very hard, woody stems that have distinct trunks and are densely branched. Mango and Eucalyptus are two examples.
2). Weak stem:-
A weak stem refers to an aerial stem that is unable to remain upright. It consists of the following type
a) Creeper: ‘Creeper’ refers to the weak stem that grows horizontally on the soil surface. Example Sweet potato,
b) Decumbent stem: Prostrate stem with vertical top.
c) Climber: ‘Climbers’ are weak stems that climb onto other erect supports with the help of unique structures formed on them. Betel, Pothas, etc (Money plant).
1. Cylindrical stem: A stem that resembles a cylinder. Four angled stems make up a quadrangular shape.
2. solid: When the container is totally filled. The middle region of the fistula is hollow. At nodes, discrete joints can be visible.
3. Herbaceous: A soft herbaceous plant. Hard, Woody. Branched stem: a stem having numerous branches.
4. Weak: A stem that cannot stand on its own.
5. Glabrous: Stem with a smooth surface.
6. Pubescent: hairy protrusion on the stem.
Functions of stem:-
1. The stem provides support for branches, leaves, flowers, and fruits.
2. It transports water and minerals from the roots to various areas of the shoot system, as well as food from the leaves to the roots.
3. Photosynthesis is carried out by the stems of some plants.
Modifications to the stem
Modifications to the shoot system:- ‘Stem modification’ refers to any alteration in the usual form and structure of a shoot or its sections in response to a plant’s demand.
There are three varieties of it.
1. underground stem. 2) Aerial stem modification and 3) Sub-aerial stem modification
1. Modification of underground stems for food storage, vegetative propagation, and perennation
There are four different types of it. They are as follows: – A.Rhizome B.Tuber C.Corm, D.Bulb
A.Rhizome
The rhizome is a modified underground stem that develops horizontally beneath the soil surface. It is made up of the number of nodes and internodes in the network. Scales can be found at nodes. The axillary bud is present in the axil of the scale leaf and at the apex of the Rhizome Terminal bud. Adventitious roots can be found on the bottom surfaces of the Nodes. The terminal bud becomes a Leafy shoot, while the axillary bud becomes a daughter Rhizome. These severances from the mother plant grow into a separate plant. Turmeric, ginger, etc.
B. Tuber
Just below the soil surface, the tuber is a bulged tip of the stem’s lowermost branches. Nodes are represented by the eyes on the tuber. Each Eye is made up of a scale leaf with a decreased axil and an axillary bud. The axillary develops into the daughter plant when the Tuber’s Eyes break from the mother Tuber and are planted in damp soil. Potato, as an example.
C. Corm
The corm is a stem that grows underground. It grows vertically beneath the soil and is thick, fleshy, and spherical in shape. Scale leaves grow on it. Axillary buds can be found in the axils of scale leaves. Adventitious roots can be found on the bottom surface. Leafy shoot develops from a single terminal bud. After separation from the mother plant, the axillary bud grows into a daughter corm, which then develops into an independent plant. Amorphophallus, for example (Yam)
D. Bulb
The bulb is a modified subterranean stem used for food storage and vegetative propagation. The bulb stem is compressed into a Disc-like shape in Bulb. A number of adventitious roots grow from its lower surface, and concentrically arranged fleshy scale leaves grow from its upper surface. An axillary bud is present in the axil of the Scale leaf, and a terminal bud is present in the middle region.
The flowering branch originates from the terminal bud, whereas the daughter buds emerge from the axillary bud. This develops into an independent plant after being separated from the mother bulb. For example, Allium cepa (Onion).
II By Sub-aerial stem
The stem of some plants grows horizontally just above or below the soil. They’re mostly intended for vegetative propagation. There are four types in all. They are as follows: –
A.Runner
The runner is a modified sub-aerial stem for vegetative proliferation. A long, slender branch serves as the stem. creeps across the soil’s surface It grows shoots above and adventitious roots below each node. When removed from the mother plant, they grow into their own plant. Example Oxalis
B. Stolon
Metha (Pudina) Stolon is a vegetative propagation modified sub aerial stem. It’s a long, elongated structure that grows upwards, bends down, touches the soil, and generates roots and leaves on both sides. This develops into an independent plant after being separated from the mother plant. Example Colocasia,
C. Sucker
Sucker is a sub-aerial stem that has been modified. It’s a lateral branch that emerges from the underground stem obliquely below the soil. It grows into a shoot when it rises above the soil’s surface. It develops into an individual plant once it splits from the mother plant. The aerial shoot system has been adapted to fulfill many activities such as protection, climbing, photosynthesis, vegetative propagation, and so on. Example Chrysanthimum
D. Offset
In Hydrophytes, an offset is a modified sub-aerial stem (Plants growing in water). The short, stout, prostrate branch that shoots in all directions from a mother plant is known as an offset. This develops into an independent plant after being separated from the mother plant. Example Pistia, Eichhornia
III. By Aerial stem
The stem grows above the soil surface in aerial stem modification. Protection, climbing, photosynthesis, vegetative propagation, and other tasks are performed by modifying the entire stem or distinct portions of the stem. There are five different types of it. The following is a list of them: Bulbil, stem tendril, stem thorn, phylloclade, Cladode
1.StemTendril
Tendrils are coiled modified structures that are sensitive to contact and are long, slender, and coiled. They aid the plants in their ascent.
1. The terminal bud of Vitis quadrangularis is transformed into Tendril.
2. The axillary bud of the Passion flower (Passiflora) gets transformed into Tendril.
2. Thorns are hard-pointed structures that have been adapted to give protection.
For example, the axillary bud of Canthium is transformed into a thorn, while the terminal bud of Carrisa is transformed into a thorn.
3. Phylloclade
Phylloclade is a photosynthetic structure that is green, fleshy, cylindrical, flattened, or spherical. To reduce transpiration, leaves at nodes are transformed into spines or scales. Opuntia, for example (Prickly pear).
4. Cladode
Cladode is a photosynthesis-oriented tiny, green, flat, leaf-like modified lateral branch with only one or two internodes. The leaves have been shrunk down to minute scales. Asparagus is a good example.
5. Bul-bil
Bulbils have bulged vegetative or floral buds that are used to propagate plants. For example In Agave Floral Buds.