Translocation of organic material is best explained by

The translocation of organic material is best explained by the Mass flow hypothesis.
The mass flow hypothesis was proposed by Ernst Munch, a German plant physiologist in 1930. It explains the movement of sap through the phloem.
While the movement of water and minerals through the xylem is driven by negative pressures (tension) most of the time, movement through the phloem is driven by positive hydrostatic pressure. This process is termed translocation and is accomplished by a process called phloem loading and unloading.