Shoot subapical cells in the parasitic angiosperm Cuscuta japonica seedlings were ultrastructurally studied. Seedlings were grown for 3 d in the dark and then for an additional 3 d in sunlight. Under either type of illumination, most cells in the primary meristem contained several vacuoles with or without electron-dense particles. These vacuoles were believed to be derived from degraded protein bodies with globoid crystals that were stored in the embryos. As growth progressed, the reserves were gradually depleted, while various cell organelles increased. This indicated that those storage reserves were utilized for seedling development and that, concurrently, cellular metabolism in the seedling cells converted from a quiescent to an active state. When seedlings were exposed to sunlight, etioplasts with prolamellar bodies developed into chloroplasts possessing thylakoids that were well-organized into grana. These observations suggest that C. japonica seedlings might exist autotrophically and photosynthesize during a free-living stage prior to parasitizing their hosts.