In the dichotomously branched caulerpalean green algaChlorodesmis fastigiata long range cytoplasmic streams run through the siphon and form a network of shorter strands in the region of the bulbous enlargement of the dichotomies. Continuous transport of organelles occurs along these streams, which are contructed of a central bundle of microtubules, around which the organelles are grouped. Both chloroplasts and amyloplasts exhibit a unique dorso-ventral symmetry: their flattened ventral side is closely apposed to the surface of the microtubule bundles. The concentric lamellar system (CLS) at the tip of the plastids invariably points in the direction of movement. These findings are discussed in relation to microtubule based motility. It is suggested that the unique plastid architecture serves as an efficient differentiation facilitating long range transport along the microtubule bundles.