Fig. 3

The ovule and seed development of Vanilla planifolia. A The archesporial cell enlarges and differentiates into the megasporocyte (*). At the same time, the inner integument (arrowhead) has become visible. Scale bar = 30 μm. B Light micrograph showing an expanding four-nucleate embryo sac by vacuolation. The inner integument (arrowhead) has completely enclosed the embryo sac, and the multilayered outer integument (arrows) is expanding. Scale bar = 30 μm. (C) A mature embryo sac showing the egg apparatus (*), including the egg cell and two synergids. The outer integument (arrow) continues to elongate; moreover, it has not enclosed the inner integument (arrowhead). Scale bar = 30 μm. D After fertilization, the zygote (*) has a dense cytoplasm, and the degenerated antipodal cells (double arrowhead) at the chalazal end are also densely stained. At this stage, the cytoplasm of the inner seed coat (arrowhead) remains densely stained, and the walls of the outermost layer of the outer seed coat (arrow) become thickened. Scale bar = 30 μm. E Light micrograph showing a cross-section of a fertilized ovule showing the distinct layers of the inner seed coat (arrowhead) and outer seed coat (arrow). Scale bar = 30 μm. F Light micrograph showing a three-celled proembryo (*), and the developing seed attaches to the placenta through the funiculus (double arrowhead). The inner seed coat (arrowhead); The outer seed coat (arrow). Scale bar = 30 μm. G Light micrograph showing an early globular embryo without a distinct suspensor during embryo development. At this stage, the inner seed coat (arrowhead) gradually compresses. The outer seed coat (arrow). Scale bar = 30 μm. H Light micrograph showing a globular embryo. At this stage, the inner seed coat (arrowhead) has shriveled, and the outermost layer of the outer seed coat (arrow) has become lignified. Scale bar = 30 μm. I At maturity, numerous tiny protein bodies are found within the embryo proper cells. In this preparation, the lipid bodies are not preserved; storage lipid bodies occupy the spaces between the protein bodies. The inner seed coat (arrowhead) has compressed into a thin layer, and the outermost layer of the outer seed coat (arrow) has lignified and been filled with dark material. Scale bar = 30 μm