The pressure-flow hypothesis describes

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The pressure-flow hypothesis describes how carbohydrates in solution move through the phloem, from a source (usually leaves) to a sink (usually roots or growing tissues). It involves the formation of a pressure gradient between source and sink, which drives the movement of carbohydrates from high pressure to low pressure areas. This process requires energy and is facilitated by specialized cells called sieve tubes and companion cells. The pressure-flow hypothesis does not apply to water and minerals in the xylem, which are moved primarily by transpiration and root pressure. Hormones may be transported in the phloem, but the pressure-flow hypothesis does not specifically explain their movement.

The Pressure-Flow Hypothesis Describes