Fig. 8

The seed coat development of Vanilla planifolia. A The seed coat consists of an inner seed coat (IS, two cells thick) and an outer seed coat (OS, three to four cells thick). At the time of fertilization, the cell wall of the outermost layer of the outer seed coat remained primary in nature. Scale bar = 20 μm. B In the globular embryo stage, the cell wall of the outermost layer of the outer seed coat (OS) thickens, and the inner seed coat (IS) becomes dehydrated and compressed. Scale bar = 20 μm. C As the seed matures, the thickened outermost layer of the outer seed coat and the inner layers gradually dehydrate and compress. The inner seed coat (IS) has compressed into a thin layer at this stage. Scale bar = 20 μm. D At maturity, both the thin inner seed coat (IS) and the thickened outer seed coat (OS) compress and envelop the embryo E tightly. Scale bar = 20 μm