Phloem is like plant’s version of blood-it transports nutrients up and down the plant. Extra phloem is sent to the roots for storage. Force is generated at the source-where the nutrients are going (also by where they are coming from). Phloem forces are positive pressure. The destination generates pressure lower than source-all positive pressures, no tension. Phloem cells are much smaller and have thinner cell walls than xylem. The outer part of phloem gives structure-bundle sheath. The primary phloem is the first phloem-first formed. The secondary phloem is made after primary a d comes after vascular cambium. In between shoot meristem and root meristems are primary tissues, xylem and phloem differentiate after these points. In a tree, a new meristem differentiates in the trunk-this is the cambium which makes new cells (trees).
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