Selection of proper tissue is very important when repetitive embryos are subcultured, especially if transformation is a goal. The most transformable tissue consists of numerous, small globular-stage embryos tightly packed together, looking like a minature, green raspberry. The photo below indicates the tissues which would be subcultured, either for transformation, or for the intiation of repetitive cultures:
For more information, see:
C. B. Hazel, T. M. Klein, M. Anis, H. D. Wilde, and W. A. Parrott. 1998. Growth characteristics and transformability of soybean embryogenic cultures. Plant Cell Rep. 17:765-772.