Plastid envelopes in reproductive cells.

During oogenesis in the fern Paesia the plastid envelopes become progressively less distinct following aldehyde fixation and osmication, but react normally to permanganate. Consideration of the formation of the membrane image by osmium and by permanganate leads to the conclusion that the lipids of the envelope membranes become less unsaturated as the egg matures. This may increase permeability of the envelope and facilitate metabolic interchange with the ground cytoplasm. The mitochondrial envelopes remain unchanged throughout oogenesis. Similar behaviour of the plastid envelope has been observed during the differentiation of other reproductive cells, both spores and gametes.