Phloem is the complex tissue used in the transport of organic food materials from leaves to stem and roots in a downward direction. It consists of the following elements: Sieve element (long tube-like cells placed end to end, forming a continuous channel with perforations and hence called sieve tubes), companion cells (thin-walled, more or less elongated cells and which are associated with sieve tubes with a prominent nucleus and are, therefore, living in nature), phloem parenchyma (elongated with rounded ends and possess cellulosic cell walls and the cells are living and store food reserves in the form of starch and fats), and phloem or bast fibers (elongated lignified sclerenchymatous cells with tapering ends and with simple pits, non-living cells that provide mechanical support to the organs).