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The basic function of the xylem is to transport water upward from the roots to parts of the plants such as stems and leaves, but it also transports nutrients. [ 1 ] [ 2 ] The word xylem is derived from the Ancient Greek word, ξύλον ( xylon ), meaning "wood"; the best-known xylem tissue is wood , though it is found throughout a plant. [ 3 ]
The xylem is oriented toward the adaxial surface of the leaf (usually the upper side), and phloem is oriented toward the abaxial surface of the leaf. This is why aphids are typically found on the undersides of the leaves rather than on the top, since the phloem transports sugars manufactured by the plant and they are closer to the lower surface.
The xylem typically lies towards the axis with phloem positioned away from the axis . In a stem or root this means that the xylem is closer to the centre of the stem or root while the phloem is closer to the exterior. In a leaf, the adaxial surface of the leaf will usually be the upper side, with the abaxial surface the lower side.
3- Water moves from the xylem into the mesophyll cells, evaporates from their surfaces and leaves the plant by diffusion through the stomata. In plants, the transpiration stream is the uninterrupted stream of water and solutes which is taken up by the roots and transported via the xylem to the leaves where it evaporates into the air/ apoplast ...
Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve-tube elements. The xylem consists of vessels in flowering plants and of tracheids in other vascular plants. Xylem cells are dead, hard-walled hollow cells arranged to form files of tubes that function in water transport.
Transpiration of water in xylem Stoma in a tomato leaf shown via colorized scanning electron microscope The clouds in this image of the Amazon Rainforest are a result of evapotranspiration. Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves , stems and flowers .
The leaves draw water from the ground in the transpiration stream through a vascular conducting system known as xylem and obtain carbon dioxide from the atmosphere by diffusion through openings called stomata in the outer covering layer of the leaf , while leaves are orientated to maximize their exposure to sunlight.
The numerous leaf gaps and leaf traces give a dictyostele the appearance of many isolated islands of xylem surrounded by phloem. Each of the apparently isolated units of a dictyostele that serve a single leaf can be called a meristele. [11] Among living plants, this type of stele is found only in the stems of ferns.