Stem and Xylem Adaptations
Stems are important for a plants structure and the transportation of resources such as water and food. The stem is made up of vascular bundles which consist of xylem and phloem (water and food respectively).
Because some xerophytes have limited or no leaves, the stem is the site of photosynthesis, therefore the stem is the most important part of the plant in a non-leaved xerophyte. To help with transpiration these plants can have little hairs on them which are where the water evaporates out. A xerophytes stem is wood-like and very strong and has a lot of tissue mass instead of xylem vessels so that if there is an influx of water, the plant is able to store it and save it for growth later on.
Most hydrophytes are supported by the water around them so there is no need for them to have big strong stems. Some hydrophytes can be found to have hollow, floppy stems containing next to no lignin in them. Lignin is found in the xylem vessels and are used to strengthen them. As water can be soaked in almost anywhere in a hydrophyte, it is not necessary to have lots of xylem in the plant. Hydrophytes have a better water balance then, as they can more easily control the amount of water that comes in to the plant, therefore less risk of the plant drowning.
Unlike hydrophytes, mesophytes can not absorb water from anywhere in the plant and so must have a well developed stem and xylem vessel system in order to transport materials (most importantly water) around the plant. The water enters the plant in the roots and then enters the xylem vessel where the adhesion and cohesion help it to travel up to the leaf where it is used for photosynthesis and gas exchange.
Because some xerophytes have limited or no leaves, the stem is the site of photosynthesis, therefore the stem is the most important part of the plant in a non-leaved xerophyte. To help with transpiration these plants can have little hairs on them which are where the water evaporates out. A xerophytes stem is wood-like and very strong and has a lot of tissue mass instead of xylem vessels so that if there is an influx of water, the plant is able to store it and save it for growth later on.
Most hydrophytes are supported by the water around them so there is no need for them to have big strong stems. Some hydrophytes can be found to have hollow, floppy stems containing next to no lignin in them. Lignin is found in the xylem vessels and are used to strengthen them. As water can be soaked in almost anywhere in a hydrophyte, it is not necessary to have lots of xylem in the plant. Hydrophytes have a better water balance then, as they can more easily control the amount of water that comes in to the plant, therefore less risk of the plant drowning.
Unlike hydrophytes, mesophytes can not absorb water from anywhere in the plant and so must have a well developed stem and xylem vessel system in order to transport materials (most importantly water) around the plant. The water enters the plant in the roots and then enters the xylem vessel where the adhesion and cohesion help it to travel up to the leaf where it is used for photosynthesis and gas exchange.