Translocation (botany)
The 'pressure flow' hypothesis was proposed by Ernst Münch in 1930 to explain the mechanism of phloem translocation. Leaves photosynthesize, making sugars. Water moves into the sugar-laden sieve-tube cells with sugar by osmosis. This creating pressure that pushes the sap down the sieve tube. When the sugar reaches cells that need it, the cells actively transport sugars out of the sieve-tube elements.