Tracers, such as radioactive isotopes, can be used to track the movement of organic substances in the plant, providing evidence for translocation.

Ringing experiments involve removing a ring of bark, which includes the phloem, from a stem.

This disrupts the phloem and thus translocation, which affects the plant's growth and provides evidence that the phloem is necessary for the mass flow of sugars.

The mass flow hypothesis proposes that translocation occurs due to pressure gradients:

1. Solutes are actively transported into sieve tube elements, causing a high hydrostatic pressure at the source
2. Solutes are moved by the phloem to respiring cells where they are removed from the sieve tube elements for use or storage, creating a low hydrostatic pressure at the sink
3. This hydrostatic pressure difference results in the mass flow of solutes through the phloem

1. Active loading at source cells - actively transporting sucrose from source cells into companion cells, and subsequently into phloem sieve tube elements for translocation
2. Active unloading at sink cells - actively transporting sucrose from the phloem sieve tube elements into companion cells, and subsequently into sink cells where it is used or stored

Sources are areas where sucrose is produced, like leaves.

Sinks are areas where sucrose is used or stored, like roots or meristems.

Other substances that are transported in the phloem, like amino acids, are also moved from sources to sinks. The locations of sources and sinks may change depending on the substance transported and the time of year.

Water provides the medium in which sugar, specifically sucrose, dissolves for transport in the phloem.

Translocation is mass flow of sucrose and amino acids from one part of a plant (the source) to another part of the plant (the sink).