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Phloem; Vascular cambium; Wood Sapwood (alburnum) Heartwood (duramen) Pith (medulla) In young stems, which lack what is commonly called bark, the tissues are, from the outside to the inside: Epidermis, which may be replaced by periderm; Cortex; Primary and secondary phloem; Vascular cambium; Secondary and primary xylem.
The trunk consists of five main parts: The outer bark, inner bark , cambium, sapwood (live xylem), and heartwood (dead xylem). [2] From the outside of the tree working in: The first layer is the outer bark; this is the protective outermost layer of the trunk. Under this is the inner bark which is called the phloem. The phloem is how the tree ...
Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem Detail of the vasculature of a bramble leaf Translocation in vascular plants. Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem ...
The fascicular and interfascicular cambia thus join up to form a ring (in three dimensions, a tube) which separates the primary xylem and primary phloem, the cambium ring. The vascular cambium produces secondary xylem on the inside of the ring, and secondary phloem on the outside, pushing the primary xylem and phloem apart.
Most of these cells transform into xylem and phloem. But certain cells don't transform into xylem and phloem and remain as such. [clarification needed] These cells cut out by the cambium towards the periphery are phloem parenchyma while those towards the pith are xylem parenchyma. Both of these cells together work as secondary medullary rays.
Since the valuable fibres are located in the phloem, they must often be separated from the woody core, the xylem, and sometimes also from the epidermis. The process for this is retting , and can be performed by micro-organisms either on land (nowadays the most important) or in water, or by chemicals (for instance high pH and chelating agents ...
This is the only type of xylem found in the earliest vascular plants, and this type of cell continues to be found in the protoxylem (first-formed xylem) of all living groups of vascular plants. Several groups of plants later developed pitted tracheid cells independently through convergent evolution .
Cork cambium (pl.: cambia or cambiums) is a tissue found in many vascular plants as a part of the epidermis. It is one of the many layers of bark, between the cork and primary phloem. The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems.