Phloem transports sugars from source to sink. Source sites include photosynthetic tissue, usually leaves, where sugars are manufactured, and storage organs (thickened stems or roots, such as the root of a sugar beet).
Vascular Plants
Freed from the requirement to hug a moist soil surface, plants with vascular tissue can grow tall, extending their complex stems and leaves into the dry air. Vascular tissue, along with several other important plant features, allowed plants to colonize Earth's surface. Today, our planet hosts an enormous diversity of vascular plant life, including such different forms as ferns, redwood trees, oak trees, and orchids.
Vascular tissue develops in all organs—root, stem, and leaf—of the plant body. In the primary plant body, vascular tissue differentiates from a primary meristem, the procambium. Xylem and phloem tissues that differentiate from procambial tissue are called primary xylem and primary phloem. In plants with secondary growth, vascular tissue differentiates from a lateral meristem, the vascular cambium, producing secondary xylem and secondary phloem. Secondary xylem is a familiar product: wood.
Xylem: the Water-Conducting Vascular Tissue
Xylem is a complex tissue composed of several different cell types.
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