Application of the technique of silicone oil centrifugal filtration has shown that for some compounds, particularly oxaloacetate and succinate, there is a pronounced increase in permeability after 1–2 h of greening. Other compounds such as malate, glycine, and glutamate are progressively less permeable during plastid morphogenesis. Alanine, aspartate, and 3-phosphoglycerate show an initial decline in permeability after 1 h illumination but ready uptake into 2–4 h etiochloroplasts. There is also evidence that a translocator system for dicarboxylic acids involving malate exists within the plastid envelopes of Avena.