How do substances move in the Phloem?
Translocation is the movement of organic solutes through plants. These solutes are generally produced at photosynthetic sites ( source) and are moved to either growing or storage sites depending on the time of the year ( sink). As growth or storage sites may exist anywhere in the plant simultaneously, flow must be able to be bi-directional within a phloem element. The first evidence that phloem carried these solutes occurred back in the 1600’s through the studies of Marcello Malphigi. When a ring of bark of striped off of a tree the tissue above became swollen, he correctly interpreted this to mean that the solute solution coming from the leaves above was trapped by the break in the bark. This phenomenon of stripping is called girdling and is used to kill trees. Unintentionally it also occurs when animals such as deer desperate for food in the winter eat bark and then kill off the trees. In 1800s Theodore Hartig, a German botanist studied the same phenomenon. Through an anatomical anal
