Secondary Phloem

Definition - What does Secondary Phloem mean?

In plant biology, the secondary phloem is a part the cambium vascular growth of a tree or woody plant. It is the food-conducting tissue and is sometimes referred to as the tree’s inner bark, which is where it is located.

The secondary phloem lies towards the outside of the cambium layer and is actually produced by the tree’s cambium. As the tree grows, it produces yearly layers of secondary phloem and secondary xylem that are visually distinguishable if the tree’s trunk is cut in half.

MaximumYield explains Secondary Phloem

The vascular cambium growth is what forms the secondary xylem and the secondary phloem. Both are what compose the telltale rings of a tree and can be used to tell the tree’s age because each ring represents a year of the tree’s life.

The vascular cambium’s secondary xylem is located inwards toward the tree’s pith and the secondary phloem is situated beside the bark. The main function of secondary phloem is to transport nutrients throughout the tree or woody plant. As the vascular cambium produces more secondary xylem, the older, more exterior portions of the secondary phloem are crushed. They die, and are sloughed off as part of the bark.

Phloem, in all vascular plants, is the living tissue that transports the soluble organic compounds made during photosynthesis to various parts of the plant. It consists of conducting cells, parenchyma cells, and supportive cells, such as fibers and sclereids. The secondary phloem of angiosperms consists of:

  • sieve-tube members
  • companion cells
  • scattered parenchyma
  • ray parenchyma
  • fibers (usually occurring in clusters alternating with the sieve tubes and parenchyma cells)
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