Phloem is a complex tissue found in higher plants, consisting of several types of cells that work together to transport nutrients and organic compounds throughout the plant. The main constituents of phloem are:
- Sieve tubes: These are elongated cells that form the main conduits for the transport of nutrients and organic compounds. Sieve tubes are connected end-to-end to form a continuous tube-like structure that runs through the plant.
- Companion cells: These are specialized cells that are closely associated with sieve tubes and provide metabolic support to them. Companion cells are responsible for loading and unloading nutrients and organic compounds into and out of the sieve tubes.
- Phloem fibers: These are long, thin cells that provide structural support to the phloem tissue. Phloem fibers are composed of cellulose and lignin, which make them strong and resistant to bending.
- Phloem parenchyma: These are relatively unspecialized cells that fill the spaces between the other phloem cells. Phloem parenchyma cells have a variety of functions, including storage and support.
Overall, the constituents of phloem work together to transport nutrients and organic compounds from sources (such as leaves) to sinks (such as roots, developing fruits, or growing buds) throughout the plant.