Figure 2

Developmental stages of the embryo sac in Populus simonii × P. nigra var. italica (bar = 10 μm). (A) A uni-nucleate embryo sac; (B) A two-nucleate embryo sac; (C,D) A four-nucleate embryo sac (serial section); (E,F) An eight-nucleate embryo sac (serial section).