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Primary xylem is formed during primary growth from procambium. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. Metaxylem has wider vessels and tracheids than protoxylem. [citation needed] Secondary xylem is formed during secondary growth from vascular cambium.
Much lateral branch systems would, indeed, be very similar to those of conifers. Leaf and branch trace formation-The protoxylem regions are radially elongate, and except in regions just above levels of leaf trace divergence consist of two protoxylem poles connected by a sheet of protoxylem tracheids mixed, apparently, with parenchyma.
Xylem is the water-conducting tissue, and the secondary xylem provides the raw material for the forest products industry. [26] Xylem and phloem tissues each play a part in the conduction processes within plants. Sugars are conveyed throughout the plant in the phloem; water and other nutrients pass through the xylem.
In the stems of some Asterales dicots, there may be phloem located inwardly from the xylem as well. Between the xylem and phloem is a meristem called the vascular cambium. This tissue divides off cells that will become additional xylem and phloem. This growth increases the girth of the plant, rather than its length.
Inside the phloem is a layer of undifferentiated cells one cell thick called the vascular cambium layer. The cells are continually dividing, creating phloem cells on the outside and wood cells known as xylem on the inside. [67] The newly created xylem is the sapwood. It is composed of water-conducting cells and associated cells which are often ...
The xylem system is seen to develop in this zone along with lateral root development. Elongation Zone: Cells in this stage are rapidly elongating and parts of the phloem system (sieve tubes) start to develop. As you move up closer to the maturation zone, cell division and, elongation decrease.
Cross-section of a flax plant stem: 1. Pith 2. Protoxylem 3. Xylem I 4. Phloem I 5. Sclerenchyma 6. Cortex 7. Epidermis. In botany, a cortex is an outer layer of a stem or root in a vascular plant, lying below the epidermis but outside of the vascular bundles. [1]
The presence of vessels in xylem has been considered to be one of the key innovations that led to the success of the flowering plants. It was once thought that vessel elements were an evolutionary innovation of flowering plants, but their absence from some basal angiosperms and their presence in some members of the Gnetales suggest that this hypothesis must be re-examined; vessel elements in ...