Different types of plasmodesmata in the transport phloem. A, C. maxima; plasmodesmata between the SE and CC (PPUs) and between the CCs. In the PPUs a single pore on the SE side (arrowhead) is jointed with the plasmodesmal branches on the CC side, which resemble the plasmodesmal branches (arrows) between the CCs. B, Z. elegans; in contrast to the usual orientation, the PPU appears to have the furcating plasmodesmata at the SE side and the single pore end to the CC side. Bar: A, 0.5 μm; B, 100 nm.