ONTOGENY OF SOMATIC EMBRYOS OF PENNISETUM-AMERICANUM .2. IN CULTURED IMMATURE INFLORESCENCES

Embryogenic callus was induced from young, unemerged inflorescences of P. americanum cultured on Murashige and Skoog''s medium supplemented with different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D). The amount and quality of the embryogenic callus and the rapidity with which it was formed depended on the age of the explant and the concentration of 2,4-D. Best results were obtained from explants with floral primordia at the earliest stages of development and with 2.5 mg/l 2,4-D. The compact embryogenic callus originated from the floral primordia. Subsequent differentiation of the callus led to the formation of subepidermal layers of embryogenic cells. These richly cytoplasmic cells contained numerous starch grains. Increase in cell wall thickness, cell separation, and a sequence of internal segmenting divisions in single embryogenic cells led to the formation of embryoids.