What is plant stem?
The plant stem is the ascending axis of the vascular plant they walloping from the plumule of a germinating seed, which is positively phototropic and performs the functions of mechanical support, conduction of water and translocation of food.
The second major branch that emerges from a germinating seed is the plumule, which develops to form the shoot and is positively phototropic except the underground modified stems. The plant stem represents the upper part of the plant axis, which is negatively geo-tropic and hydrotropic in nature. The branches of the stem along with the leaves, auxiliary buds compose the shoot system of the plant.
Important Characteristics of Stem:
From the plumule of the embryo of a germinating seed the plant stem develops. It is the ascending axis of the plant and usually positively phototropic and negatively geotropic in nature. The plant stem supports the leaves, flowers and fruits. The apical part of the plant stem contains the apical bud, and it helps in vegetative growth, while the axils of the leaves contain the axillary buds, that may either produce the branches or act as reproductive structures. The region from where the leaves come out the nodes while the region remaining in between is the inter-node.
The branches come out exogenously to produce a massive, dendrobial structure. The plant stem in young stage is green in color due to presence of chlorophyll, helping photosynthesis and in the latter stage it becomes woody. On the basis of their hardness, the plant stem classifies the plant into herb, shrub and tree.
The plant stem may have different forms such as, square, triangular, jointed or ribbed and the surface may be smooth, hairy or with prickles of protection. It may be strong and weak and are classified into several sub types in this basis.
The normal functions of the plant stem include mechanical support, conduction of water and food translocation. It may be modified into different types like underground, sub- aerial and serial, performing various special types of functions like storage, photosynthesis, vegetative propagation etc.
Parts of Plant Stem:
The following parts are consisting by the plant stem:
i) Nodes : It is the swollen, ring like joints occurring at a regular intervals on a stem and the leaves develop from these nodes.
ii) Internodes: In between the two nodes, the un-swollen cylindrical parts of the stem are called internodes. No lateral structure develops from the internodes, but it only helps in the apical growth of the plant via the intercalary meristem.
iii) Leaf: The leaves of the plant are the flattened, lateral organs of limited growth, which appear from the nodes and is the seat of photosynthesis. Buds may arise from the axils of leaves which are called the axillary buds.
iv) Buds: The buds are developing on the plant stem has the specialized structure consisting of a elementary stem covered with immature leaves. The buds developing on tht shoot apices are called apical buds, which help in apical growth, while the buds are developing from the axil of the leaves are called axillary buds, that may act as reproductive structures.
v) Axil : The angle formed by the leaf with the main plant stem is the axil and the axil contains the axillary buds.