Hydrophytes
The stem and xylem adaptations in hydrophytes are not to enhance its abilities of transporting water and minerals around the plant, providing a structural support or to store water, but to absorb nutrients directly from the surrounding water and to be flexible enough to move with the surrounding water while providing enough support for the plant. (NinErrin, 2015 )
The stem and the vascular bundle system is poorly developed in all hydrophytes as there is no need for mechanical strengthening tissues ( e.g. sclerenchyma) as they are mostly always supported by the water around them. If they did have fully developed stems and xylem like plants on ground with sclerenchyma tissues, it would be a disadvantage as it will make the stems rigid making it much more fragile and easy to break in the moving water. Because of this, hydrophytes, unlike plants found on land don’t go through secondary growth which would make their stems and roots thicker. (mhhe, 2015)
Xylem which is the vascular bundle that transports water and minerals throughout the plant is reduced if not absent as cells on the surface of the plant can absorb water, minerals, and dissolved gasses directly from the surrounding water meaning that hydrophytes don’t need to rely on the xylem as much as plants on land do to transport water around the plants. Even if the xylem is present, it is found at the centre of the stem to allow maximum flexibility. Hydrophytes have spongy stems due to a well developed aerenchyma in the stems that provides structural support, buoyancy and creates an internal atmosphere. Some plants even have stems that are hollow to further enhance those characteristics. (NinErrin, 2015 ) (MediaDigital, 2015) (HenryEllen, 2015) (snmichaels, 2015) (BarnesEric, 2015)
This means that when the plants are taken out of the water, it will droop as it lacks most of the internal strengthening mechanism and has a reduced water transport system meaning that it won't be able to survive for long on land or when there is no water in abundance.
(MediaDigital, 2015) (SinghKalpana, 2015) |