THE INITIATION AND DEVELOPMENT OF BROWN SALWOOD (ACACIA MANGIUM WILD) FLOWER

Abstract

Study on the initation and development of Acacia mangim flower was carried out at the field station of ASEAN-Canada Forest Tree Seed Centre by means of periodical observation and microtechnical investigation. The paraffin embedding method was used in specimen preparation. It was observed that A. mangium starts flowering firstly at the age of about 2-3 years, generally, it flowers once a year in August or September within duration of about 1 month. Reproductive buds continuously develop from lateral bud at terminal branch position. Various periods of development of inflorescene can be divided into 6 distinguished stages. The inflorescene is spike, white color with fragant. Each complete flower composes of 5 sepals, 5 petals and one-locular ovary surrounded by about 70 stamens. The locule contains 14 anatropous ovules which arranged as marginal placentation. The flower primodia occured on spike after bracts had already appeared. They develop into calyx. corolla, androecium and gynoccium repectively. The development from flower primodia to anthesis stage takes about 51 days. With careful investigation, it shows that the inflorescene opens simultaneously once a day in the early morning around 5.00-6.00 AM. and reach receptive stage 2 hours later. After fertilization, the zygote always locates at the micropylar end and endosperm develops into 2 cells. Because of unsuitable weather in winter, both egg and endosperms remain dormant about 70-75 days. At the same time, inner and outer integuments enlarge covering the embryo sac rapidly. In fertilized flowers, the petals, stamens and style will absciss whereas the ovary turns to be green and elongates into pod conspicuously.