Introduction
The stem can also store food, and healthy stems themselves manufacture food. In most plants the stem is the major vertical shoot, in some it’s inconspicuous, and in some other plant’s stem that grows underground may appear as its roots.
The primary functions of the stem are to support the leaves; to transport water and minerals to the leaves, wherever they will be regenerated into the usable product by photosynthesis; and to move this product from the leaves to different elements of the plant, together with the roots. The stem conducts water and nutrient minerals from their part of absorption within the roots to the leaves using various vascular tissues within the xylem. The movement of synthesized foods from the leaves to alternative plant organs happens principally through alternative vascular tissues within the stem known as phloem. Food and water also are at times kept within the stem. Samples of food-storing stems embody such specialised forms as tubers, rhizomes, and corms and also the woody stems of trees. Water storage is developed to a high degree within the stems of cacti, and almost every healthy stems are capable of photosynthesis.
Structure of a stem
Stems are usually structured of 3 tissues:
- Dermal tissue – The dermal tissue covers the outer surface of the stem and typically functions to waterproof, defend and manage the gas exchange. The dermal tissue of underwater plants stems could lack the waterproofing found in underwater stems.
- Ground tissue – the ground tissue typically consists of the Core of parenchyma cells and fills in around the vascular tissue. It generally functions in photosynthesis.
- Vascular tissue – vascular tissue makes long-distance transport and structural support. Most of all ground tissue could also be lost in woody stems. . The position of the vascular tissues varies widely among plant species.
Dicot stems
Dicot stems with primary growth have a pith in the middle, with vascular bundles creating a definite ring seen once the stem is visible in cross-section. The surface of the stem is roofed with a cuticle that is roofed by a water-resistant cuticle. The cuticle also could contain stomata for gas exchange and multicellular stem hairs known as trichrome. A cortex consisting of layer (collenchyma cells) and endodermis (starch-containing cells) is there on top of the pericyclic and vascular bundles.
Woody, as well as non-woody dicots, have secondary growth originating from their lateral or secondary meristems: the vascular cambium and also the cork cambium or phellogen. The vascular cambium forms between the xylem and phloem within the vascular bundles and connects to make a cylinder. The vascular cambium cells divide to supply xylem tissue to the inner part and secondary phloem to the outer part. Because the stem will increase in diameter due to the increase of secondary xylem and secondary phloem, the cortex and cuticle are eventually destroyed. Before the cortex is destroyed, a cork cambium develops there. The cork cambium divides to supply waterproof cork cells outwardly and generally phelloderm cells internally. Those 3 tissues type the periderm that replaces the epidermis in work. Lenticels are the loosely packed cells in the periderm that helps in the exchange of gases.
Monocot stems
Vascular bundles are there throughout the monocot stem, though focused towards the outer part. This differs from the dicot stem that includes circles of tube bundles and sometimes nothing. The shoot apex in monocot stems is additionally elongated. Leaf-sheaths grow old around it, protecting it. This can be taken up to some extent of just about all monocots. Monocots hardly manufacture secondary growth and are so seldom woody, with Palms and Bamboo being recognisable exceptions. However, several monocotyledons stems increase in diameter via abnormal secondary growth.
Gymnosperm stems
All gymnosperms are depicted as woody plants. Their stems look alike in structure to woody dicots except that almost all gymnosperms manufacture solely tracheids in their xylem, not the vessels found in dicots. Gymnosperm wood may typically contain rosin ducts. Woody dicots are known as hardwoods, e.g. walnut oak and Maple. In distinction, softwoods may be gymnosperms, like spruce, fir, and Pine.
Fern stems
There are no vertical stems on ferns having rhizomes. The tree ferns are an exception as they have vertical stems up to about 20 metres. The stem anatomy of fern plants is harder than that of dicots as a result of fern stems typically having one or additional leaf gaps in cross-section. A leaf gap is wherever the plant tissue branches off to a leaf. In cross-section, the vascular tissue doesn’t make an entire cylinder wherever a leaf gap happens. Fern stems could have solenosteles or dictyosteles or other varieties of them. Several ferns stems have phloem tissue on each side of the xylem in cross-sectional.
Growth and anatomy
The growing portion at the topmost of the shoot is the primary bud of the plant, and by the continuing development of this bud and its adjacent tissues, the stem will increase upwards. Lateral buds and leaves grow out of the stem at intervals known as nodes; the intervals on the stem between the nodes are known as internodes. The quantity of leaves that seem at a node depends on the species of plant; one leaf per node is common, however, 2 or additional leaves could grow at the nodes of some species. Once a leaf drops off a stem at the top of a season, it leaves a scar on the stem owing to the cut of the tube (conducting) bundles that had connected stem and leaf. Because the stem continues to grow, lateral buds are being made that would be converted into lateral shoots more or less resembling the parent stem, and these ultimately depict the branching of the plant.
Conclusion:
Thus stem system depicts the shoot system of a plant. The length of the stem may vary from plant to plant beginning from a few millimetres to hundreds of meters. Stems can be hard or soft. Their function is to hold leaves, give support to the plants, and hold flowers and buds.