Sunday, June 3, 2012

Plant Vascular Tissue

Vascular tissue is the distinguishing feature of higher plants. It is an intricate network of internal plumbing that runs continuously from the tips of the leaves and buds through the stem and main root down to the smallest root. It is visible in leaves as the familiar "veins". The two kinds of vascular tissue in plants are the xylem and phloem. Xylem transports water and dissolved minerals upward in the plant body and also supports the plant body; it is a complex tissue composed of several types of cells which form a series of minute continuous tubes from the roots, through the stems to the leaves. Several kinds of cells that make up the xylem secrete a thick secondary wall and do not perform their conducting and supporting functions until they die.

Phloem transports organic materials manufactured by the plant, such as sugars (carbohydrates) and amino acids, down from the leaves where the food was produced toward the roots and other food-consuming tissues. It also carries food materials up the plant body. Like xylem, phloem provides a continuous transport system from leaves to roots; it is also composed of several kinds of cells.