What is phloem?

What Does phloem Mean

Before entering fully into the meaning of the term phloem, it is necessary to proceed to discover its etymological origin. In this case, it must be stated that it derives from the Greek, specifically from the word "phloios", which can be translated as "bark".

This word in question was shaped by a famous Swiss botanist named Karl Wilhem von Nageli (1817 - 1891). Specifically, he created it in 1873.
The concept of phloem refers to the tissue of certain plants whose function is to conduct certain substances through these organisms. This conduction tissue allows the transfer of nutrients produced by the autotrophic and photosynthetic sector of vascular plants (the aerial part) to the heterotrophic and non-photosynthetic sectors (the underground part).
It is possible to differentiate between primary phloem and secondary phloem . The primary phloem has its origin in the procambium, which is part of the meristem or meristem (the embryonic tissue that has the ability to appeal to continuous divisions to originate other specialized tissues). In turn, it is divided into protofloem (which matures while the plant is still growing ) and metaphloem (which completes its maturation when the plant has completed its growth in length).

The secondary phloem, on the other hand, arises in the cambium, which is another kind of meristematic tissue. This phloem has a radial system and an axial system.
At a general level, the phloem is made up of various types of cells . Specifically, we can establish that the phloem is made up of four different types of cells. We are referring to the following:

-Sclerenchymal cells or elements, which act as support and can be of two kinds: fibers, which are longer in the primary phloem and shorter in the secondary, and sclereids, which have the particularity that they can be presented alone or with fibers.

-The cells or sieving elements, which are responsible for conducting organic nutrients over a long distance. Of this type are the members of the sieve tubes and the sieve cells.

-The glandular and idioblast elements, whose functions are to act as a deposit and also to undertake the secretion.

-The parenchymal elements. We have to establish these phloem cells that they are responsible for storage and also for carrying out the loading and unloading of the sieve tubes. In this group are albuminous cells, companion cells, radial parenchymal cells, and axial parenchymal cells.
It is important to distinguish between phloem and xylem . Both are vascular tissues, although they have different structures and functions. Together they make up the so-called vascular bundles: in the internal part of the bundles is the xylem, while in the external sector the phloem appears.

While phloem carries processed sap ( water with sugars, minerals, amino acids and more organic substances), xylem carries raw sap (water and salts that come from the root).

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