Answer: Lateral (sideways) movement of food at right angles to the long axis of the plant: radial translocation is along the radius of the stem/root, tangential translocation is along its circumference.
Translocation of food (organic solutes) mainly takes place up and down the plant through the sieve tubes of phloem (vertical translocation). Food also moves laterally from the phloem to the surrounding living tissues; this lateral translocation is of two types:
- Radial translocation: movement of food along the radius of the organ, i.e. from the phloem inward towards the pith and outward towards the cortex. It takes place mainly through the parenchyma cells of the medullary rays (ray parenchyma).
- Tangential translocation: movement of food sideways along the circumference of the organ, i.e. from cell to cell parallel to the surface (at right angles to both the long axis and the radius), so that tissues lying side by side in the same ring receive food.
