What is Vascular Tissue?
Vascular tissues are complex conducting tissues in higher plants that are made up of different types of cells and elements. The two main components of vascular tissue in plants are – Xylem and Phloem. These tissues are responsible for the transport of water and nutrients in the plants.
Additionally, the vascular tissues are also associated with two meristems namely – vascular cambium and cork cambium. These tissues are responsible for secondary growth in the plants. All the tissues such as xylem, phloem, cork cambium and vascular cambium constitute the vascular tissue system of the plants.
Let us look at the features of these vascular tissues.
Xylem
- Xylem is one of the conducting tissues that is responsible for the transport of nutrients and water from roots to the aerial parts of the plant such as stem and leaves.
- It is made up of specialised water-conducting cells that are known as tracheary elements.
- The first tracheary element found in xylem is tracheids. It is long and tapered and also lignified. Its primary function is to transport water and give structural support to the plants.
- Some gymnosperms and other seedless plants sometimes only consist of tracheids as their water conducting element.
- The second tracheary element found in xylem are vessel members. They are more specialised cells than the tracheids.
- Also known as vessel element, it is the primary element responsible for the transport of water in angiosperms despite the presence of tracheids. It is not found in gymnosperms.
- Apart from the tracheary elements, the xylem also consists of fibre cells and parenchyma tissue.
- The fibre cells are lignified and provide structural support to the plants. Parenchyma on the other hand are unspecialised and thin walled cells that are used for storage purposes.
Phloem
- Phloem is another conducting vascular tissue found in plants that transports food made in leaves during photosynthesis to all the parts of the plant.
- The phloem is composed of three types of cells – the conducting cells, the parenchyma cells and the supportive cells.
- The conducting cells, also called sieve elements, are composed of columns of sieve tube cells that have perforations in their lateral walls and that helps in the conduction of food throughout the plant.
- The parenchyma consists of unspecialised cells used for storage and two specialised cells namely – companion cells and albuminous cells.
- The companion cells, as the name suggests are the companion of the sieve tube cells that help in carrying out the metabolic functioning of the sieve elements.
- The companion cells are connected with the sieve tube elements by plasmodesmata.
- The albuminous cells are analogous to companion cells that are only found in non-flowering vascular plants.
- The supportive cells are sclerenchymatous cells, namely, fibres and sclereids.
- Both the cells have secondary cell walls that make them rigid and give them a high tensile strength. They are mainly present for mechanical and supportive functions.
Vascular Cambium
- The vascular cambium are unspecialised meristematic tissues that are found in between the primary xylem and primary phloem.
- Since it is a meristematic tissue, it gives rise to secondary xylem and secondary phloem.
- Unlike xylem and phloem, it is not involved in any way for conduction through the plants.
Cork Cambium
- The cork cambium is lateral meristem that is responsible for secondary growth in roots and stems of plants.
- It is usually absent in monocots, since those plants do not show secondary growth.
- The main function of the cork cambium is to produce cork that acts as a tough outer sheath for the plants.
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