Vascular Tissue Tissue System

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This includes all that tissues of the plant that function to transport materials long distances in the plant body. There are two tissue types in the vascular tissue system. Xylem transports water up the plant. Phloem transports photosynthate around the plant. Both are complex tissues in that they always have more than one cell type.

 

Xylem always includes tracheary elements. These are dead at maturity, and always have secondary walls. These also always have pits. If a tracheary element only has pits, then it is a tracheid. If a tracheary element also has perforations, then it is considered to be a vessel element. Conifers only have tracheids. Flowering plants can have both.

 

Phloem always includes sieve elements. These are alive at maturity, but are always simplified in that 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.