Evidence for movement of water through xylem If the cut end of shoot is placed in a solution of eosin dye, the dye is carried into the transport system and through to the vascular tissue of the leaves.
Lignified Xylem Vessels Lignified xylem vessels are very strong and play a very important supportive role in the stems of plants, particularly larger plants.
Why young plants wilt if water is lost from them? In smaller, non-woody plants support comes mainly from the turgid cells in the centre. This is why young plants wilt if too much water is lost.
Cambium Cambium is a layer of unspecialised cells which divide, giving rise to more specialised cells that form both the xylem and the phloem.
Translocation The movement of substances around plant is called translocation
Transpiration The movement of water in the xylem of plants depends on transpiration. Once in the leaves, water moves by osmosis from the xylem in the veins of the leaves into the mesophyll cells. Water then evaporates from the cellulose walls of the spongy mesophyll cells into the air spaces. The water vapor moves through open stomata into the external air along a diffusion gradient.
Cohesion and Adhesion Water molecules stick together one after due to cohesion. Water molecules also adhere strongly to the walls of narrow xylem vessel. This attraction between unlike molecules is called adhesion.
Cohesion and Adhesion The combination of adhesive and cohesive forces pulls the whole column of water in the xylem upwards. More water is continuously moved into the roots by osmosis from the soil to replace that lost from the leaves by transpiration.
Factors that affect transpiration Temperature Humidity Light intensity Wind