Definition of phloem
At the behest of Botany, is called phloem, tube or Liberian vessel, the conductive tissue of a plant which deals with the transport of organic nutrients, mainly, the sugars produced by the photosynthetic and autotrophic aboveground to basal underground, non-photosynthetic parts; i.e., it is that part of the central cylinder of dicotyledonous Angiosperm plants, which is specially made of bundles or packages of sieve vessels that carry the SAP down. There are two types of floemas: primary and secondary. The first is bundles vascular and mature in the parts of the plant that still grow in extension, becoming, sieve, inactive elements coming soon. It should be noted, that in those plants that do not have secondary growth, constitutes the functional phloem of adult organs. And the secondary phloem, has its origin in the cambium (specific plant tissue of woody plants), located towards the periphery of the stem or root. It has a system of axial and radial system. Meanwhile, the elements that compose the phloem are: elements sieve (the more specialized, variable thickness and side walls with nacreous thickenings are. Its function is the facilitate the Apoplast radial transport. You can see through the microscope); cell attendant (very specialized cells associated with the sieve tube. They assume the nuclear capabilities of the sieve elements and die once they cease to be functional. Dealing with the loading and unloading of sieve elements); and cells parenquimáticas (presented in a variable amount, are less specialized than the previous and present different appearances in the secondary and primary phloem. Dealing with the loading and unloading of sieve elements carrying sugar to the companion cells; they are storage of starch, tannins, fat and crystals).