原基; 胚基; 胚莖; 芽基
Blastema \Blas*te"ma\, n.; pl. {Blastemata}. [Gr. ? bud, sprout.] (Biol.) The structureless, protoplasmic tissue of the embryo; the primitive basis of an organ yet unformed, from which it grows.
blastema n : a mass of undifferentiated cells from which an organ or body part develops [also: {blastemata} (pl)]