Support in Plants – Most plants are stationary. They are not able to move like animals from one place to another. They usually prepare their food themselves during the process of photosynthesis but to fix in one place or position and to keep their whole bodies firm and erect, plants should have some supporting tissues and materials.
These tissues and materials are present in almost all parts of the body e. g. root, stem, branches, leaves etc. In stem they are in abundance. These supporting tissues keep the stem firm and other parts specially leaves in such a position to get the maximum light for carrying on photosynthesis besides performing other processes.
Supporting Tissues of Young Dicotyledonous Stem
Young dicotyledonous stem depends for its rigidity or support on the:
- Osmotic pressure and turgidity of parenchymatous tissues,
- The cylindrical distribution of its vascular bundles,
- Thick walled collenchymatous (living) and sclerenchymatous (dead) tissues.
In young dicot stem of sunflower (fig. 14.1), support is due to the cylindrical arrangement of vascular bundles near the outside of stem. Pith is present in the center while cortex is present outside the cylindrical structure. The turgidity and the osmotic properties of the parenchymatous tissues of cortex and those of pith keep the stem stiff and firm.
The parenchyma (i) becomes tightly packed and appear to serve as packing material; collenchymas (ii) in the stem of broad bean provides a flexible support and sclerenchyma (iii) thick walled, dead tissues & elongated fibres (iv) often organized in bundles, provide a relatively rigid support to the stem (fig. 14.2.).
Fig 14.2 supporting tissues of young dicotyledonous stem (i) parenchyma (ii) collenchymas (iii) sclerenchyma (iv) fibres
Spindle shaped dead thick walled tracheids and elongated fibrous cells found in xylem and phloem also provide strength to the stem (fig. 14.3).
Further Reading: Transport in Plants