Early Development of the Macadamia Ovary

Macadamia integrifolia ovaries were sampled for light microscopy from anthesis to 8 weeks after flowering. Both ovules increased in size following anthesis but only one was normally fertilized. Fertilization of one ovule appeared to inhibit fertilization of the other. The unfertilized ovule was eventually crushed by the fertilized ovule which developed a globular embryo with a short suspensor. Division of the endosperm preceded division of the embryo, and cell formation in the initially free nuclear endosperm progressed by the development of cell walls inwards from the embryo sac wall at the micropylar end of the embryo sac only. Thickenings developed on the walls of the embryo sac, persistent synergid and embryo and a hypostase developed at the base of the nucellus between the cavity occupied by the embryo sac and the integument. Both specializations are suggested to be important in the nutrition of the developing embryo. Ovaries which abscissed 4-5 weeks after anthesis had a similar anatomy to ovaries retained on the tree. Some embryos showed signs of degeneration but this was not considered to be the cause of abscission.