<P> Phloem is an equally important plant tissue as it also is part of the' plumbing system' of a plant . Primarily, phloem carries dissolved food substances throughout the plant . This conduction system is composed of sieve - tube member and companion cells, that are without secondary walls . The parent cells of the vascular cambium produce both xylem and phloem . This usually also includes fibers, parenchyma and ray cells . Sieve tubes are formed from sieve - tube members laid end to end . The end walls, unlike vessel members in xylem, do not have openings . The end walls, however, are full of small pores where cytoplasm extends from cell to cell . These porous connections are called sieve plates . In spite of the fact that their cytoplasm is actively involved in the conduction of food materials, sieve - tube members do not have nuclei at maturity . It is the companion cells that are nestled between sieve - tube members that function in some manner bringing about the conduction of food . Sieve - tube members that are alive contain a polymer called callose, a carbohydrate polymer, forming the callus pad / callus, the colourless substance that covers the sieve plate . Callose stays in solution as long as the cell contents are under pressure . Phloem transports food and materials in plants upwards and downwards as required . </P> <P> Mineralized tissues are biological tissues that incorporate minerals into soft matrices . Such tissues may be found in both plants and animals, as well as algae . Typically these tissues form a protective shield against predation or provide structural support . </P> <P> The term "tissue" comes from the French tissu, a belt of woven, and was introduced in anatomy by Marie François Xavier Bichat in 1801 . He argued that the body functions would be better understood taking as unity of study the tissues, and not the organs . Bichat distinguished 21 types of elementary tissues for the human body, a number later reduced by other authors . </P>

The type of tissue that does the work of an organ