Fig. 2

The ovule and seed development of Phaius tankervilliae. A Light micrograph of a megasporocyte. Both integuments (arrowhead) have just been initiated and become visible. Scale bar = 40 μm. B Light micrograph of a mature embryo sac. The inner integument has enclosed the embryo sac and results in the formation of a micropyle (arrowhead). The cells of the outer integument (*) have extended beyond the micropyle. Scale bar = 80 μm. C At fertilization, the pollen tube has penetrated the embryo sac through the micropyle (arrowhead). The cells of the outer integument (*) elongate further and become highly vacuolated. Scale bar = 80 μm. D The developing seed attaches to the placenta through the funiculus (arrowhead). The cells of the funiculus at the junction are small in size and will elongate as the seed develops. Scale bar = 50 μm. E Light micrograph showing a proembryo and a degenerated endosperm nucleus next to the zygote. At this stage, the inner seed coat (arrowhead) is collapsing. Scale bar = 60 μm. F A longitudinal section showing the embryo at the globular stage with an elongated suspensor (S). Scale bar = 80 μm. G The suspensor cell (S) elongates and tightly presses against the cell lining of the seed coat. Secondary walls begin to form in the outermost seed coat layer (*), while cells of the inner layer (arrowhead) remain cytoplasmic with a prominent nucleus (arrowhead). Scale bar = 25 μm. H A cross-section showing a globular embryo enclosed by the seed coat. The seed coat is composed of two cell layers. Lignin has deposited in the inner tangential and anticlinal walls of the outer cell layer (*). The inner layer will subsequently collapse and fuse with the outer cell layer. Scale bar = 100 μm. I At maturity, the seed coat (*) comprises a single layer of cells with lignified inner tangential and radial walls. Remnants of the collapsed wall from the inner integument (arrowhead) can be found outside the embryo. Scale bar = 80 μm