Xylem perforation plate

Two complex tissues, the xylem and phloem, provide the conducting network or "circulatory system" of plants. In the xylem or woody tissue, most of the cells are dead and the thick-walled tubes (tracheids) serve to transport water and dissolved minerals from the roots to the stems and leaves. The phloem cells provide the principal means of downward conduction of foods from the leaves. Phloem cells are joined end to end by sieve plates, so-called because they are perforated by numerous minute pores through which cytoplasm of adjoining sieve cells appears to be connected by strands 5-9 pm in diameter.154 Mature sieve cells have no nuclei, but each sieve cell is paired with a nucleated "companion" cell. 

A particular type of tissue is the vascular one. It contains xylem and phloem, which form bundles. Xylem is present in elongated cells with perforated end walls that no longer contain viable protoplasm. Xylem, in other words, forms open dead vessels that provide a way of transportation for minerals and water from roots to other parts of a plant. Phloem is present in elongated viable cells that have sieve end plates. Phloem translocates a solution of sugars, amino acids, and other nutritious substances. 

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