Embryo Sac and Fertilization in Cypripedium spectabile

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Abstract
The embryo sac of C. spectabile develops according to the Allium type. The first division in the lower dyad cell gives rise to the primary micropylar and primary chalazal nuclei. Of these the former divides twice to form 4 nuclei, which organize into 2 synergids, the egg cell and the upper polar nucleus. The primary chalazal nucleus usually divides only once, but sometimes one or both of the resulting nuclei divide once again, resulting in 6-, 7-, or 8-nucleate embryo sacs. In all cases one nucleus from the chalazal group functions as the lower polar nucleus. Pace''s view (1907) that the embryo sac is 4-nucleate and that during fertilisation one synergid nucleus moves downward and enters into triple fusion is considered untenable.

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