Phloem Tissue

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Phloem transports photosynthate around the plant. It is a complex tissues in that it always has more than one cell type. Phloem always includes sieve elements. These are alive at maturity, but are always simplified as their nuclei, vacuole and other cell stuctures degenerate. To survive, they must have a life-support partner cell. All sieve elements have pores connecting adjacent sieve elements. If these are restricted to specific walls that are shared by vertically arranged sieve elements, these are called sieve-tube elements. Sieve-tube elements always have companion cells for life support partners. Sieve-tube elements are found in flowering plants. The sieve elements found in conifers are sieve cells. their life support partners are albuninous cells. Other cell tyes found in phloem include parenchyma and fibers.