Direction of Translocation

Unlike the ascent of sap in the xylem, which moves strictly upward from root to shoot, the phloem is capable of translocating its organic solutes in essentially any direction the plant's needs require. Downward translocation carries food from the leaves toward the stem and roots. Upward translocation instead carries food from the leaves toward developing buds, flowers and fruits, where it supports growth, consumption and storage - the mobilisation of stored reserves during seed germination is itself a further example of this same upward-directed movement. Radial translocation moves food sideways, between the cells of the pith at the centre of the stem and the cortex and epidermis nearer the surface. This directional flexibility is a direct consequence of phloem transport always running from wherever a source organ happens …