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In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Ancient Greek word φλοιός (phloiós), meaning "bark". [3] [4] The term was introduced by Carl Nägeli in 1858. [5] [6] Different types of phloem can be distinguished. The early phloem formed in the growth apices is called protophloem.
Xylem and Phloem. A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, engages in photosynthesis, stores nutrients, and produces new living tissue. [1]
Two kinds of vascular tissue occur in plants: xylem and phloem. Phloem and xylem are closely associated with one another and are typically located immediately adjacent to each other in the plant. The combination of one xylem and one phloem strand adjacent to each other is known as a vascular bundle. [14]
Plasmodesmata are also used by cells in phloem, and symplastic transport is used to regulate the sieve-tube cells by the companion cells. [citation needed] The size of molecules that can pass through plasmodesmata is determined by the size exclusion limit. This limit is highly variable and is subject to active modification. [5]
The pericycle is located between the endodermis and phloem in plant roots. In dicot stems, it is situated around the ring of vascular bundles in the stele ...
There is also a tissue between xylem and phloem, which is the cambium. The xylem typically lies towards the axis ( adaxial ) with phloem positioned away from the axis ( abaxial ). 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.
Because calcium is phloem immobile, calcium deficiency can be seen in new growth. When developing tissues are forced to rely on the xylem, calcium is supplied by transpiration only. Boron is not relocatable in the plant via the phloem. It must be supplied to the growing parts via the xylem. Foliar sprays affect only those parts sprayed, which ...
Pteridophytes (ferns and lycophytes) are free-sporing vascular plants that have a life cycle with alternating, free-living gametophyte and sporophyte phases that are independent at maturity. The body of the sporophyte is well differentiated into roots, stem and leaves. The root system is always adventitious. The stem is either underground or ...