Fig. 5

The seed coat development of Cypripedium formosanum. A The archesporial cell (*) differentiates into a megasporocyte. Cell division (arrowhead) near the ovule's chalazal end signifies the inner integument's initiation. Scale bar = 20 μm. B Light micrograph showing the first meiotic division at the metaphase (*). At this stage, the inner integument (arrowhead) is expanding but has not enclosed the megasporocyte completely, and the outer integument has initiated (arrow). Scale bar = 40 μm. C The second meiotic division forms a two-nucleate embryo sac (*). At this stage, the inner integument (arrowhead) has enclosed the developing embryo sac completely, and the outer integument is still growing (arrow). Scale bar = 40 μm. D Light micrograph of a zygote (*) just after fertilization. The zygote is polarized with a chalazal-located nucleus and a prominent vacuole occupying the micropylar end. The embryo sac and the inner seed coat (arrowhead) have enlarged and elongated at this stage. In contrast, the expanding outer seed coat (arrow) has not enveloped the entire embryo sac. Scale bar = 30 μm. E Light micrograph of a two-celled embryo (*), and the cell division is unequal as judged from the location of the newly formed cell plate. The outer seed coat (arrow) envelopes the embryo sac at this stage. Scale bar = 30 μm. F Light micrograph of an early globular embryo. This species has a single-celled suspensor (S) that does not protrude from the embryo sac throughout embryo development. Scale bar = 30 μm. G Light micrograph showing a maturing globular embryo. At this stage, storage products, such as protein bodies, accumulate within the cells of the embryo proper. The cells of the inner seed coat (arrowhead) begin to shrivel, and the out layer of the outer seed coat (arrow) has compressed. Scale bar = 40 μm. H At maturity, the embryo proper is enveloped by the shriveled inner seed coat (arrowhead) and outer seed coat (arrow). Scale bar = 40 μm. I Light micrograph showing a longitudinal section through the inner seed coat (carapace; arrowhead) and outer seed coat (arrow) with the embryo proper removed. Scale bar = 40 μm