Abstract: Surface embryonic cells, which develop into embryoids, are gradually surrounded by active-divided non-embryonic cells and become internal embryonic cells in callus. Internal embryonic cells have the same morphology and structure with surface embryonic cells under light microscope. But there are no layer[s] of cells with the highest content of starch grains around internal embryonic cells. Internal embryonic cells divide actively to produce pro-rootcaps and eventually break up the callus to produce roots at any directions of callus. By inference, we suggest that the lost of ability of callus to differentiate partially be concerned with the unactive-division of embryonic cells and active-division of non-embryonic cells.

Key words: Rice, Callus, Internal embryonic cells