Figs. 38–45. Light micrographs showing stages of the cellularization and differentiation phases of endosperm development in Platanus racemosa. All sections are longitudinal and are oriented with chalazal end toward top of page. Figure Abbreviations: ANT, antipodal cell; CCZ, cellularized chalazal zone; EMB, embryo; N, endosperm nucleus. Arrows indicate developing cell walls. 38. Cell walls forming in chalazal zone. Scale bar = 25 µm. 39. Chalazal half of ovule in which the chalazal zone has cellularized, but the micropylar zone is still coenocytic. The antipodals are large and persistent. Scale bar = 100 µm. 40. The next phase after the chalazal zone has cellularized. Anticlinal cell walls (perpendicular to the central cell wall) forming between pairs of recently divided endosperm nuclei at the chalazal end of the micropylar zone. Scale bar = 50 µm. 41. Early phase of endosperm alveoli in micropylar zone. Scale bar = 25 µm. 42. Later alveolar stage, central vacuole is surrounded by a single layer of alveoli and cells. Scale bar = 50 µm. 43. The earliest stage of completely cellular endosperm, consisting of large, thin-walled, vacuolate cells. Scale bar = 100 µm. 44. The endosperm differentiates into an outer endosperm layer of smaller, densely stained cells and an inner endosperm of larger, vacuolate cells into which the embryo grows. The inner endosperm breaks down in advance of the growing embryo. Scale bar = 100 µm. 45. The embryo consumes the inner endosperm and is surrounded by the outer endosperm. Scale bar = 100 µm