Abstract
This investigation concerns four species: Cercis canadensis L., Cassia abbreviata Oliv. var. granitica, Cassia nictitans L., and Gleditsia triacanthos L. In Cercis canadensis the archesporium is subhypodermal and may consist of one or two cells. A single hypodermal archesporial cell develops in the other three species. The hypodermal archesporial cell in the Cassia species and in G. triacanthos divides periclinally to form a parietal cell and a primary sporogenous cell. Derivatives of the parietal cell contribute to the nucellar mass as the sporogenous cell enlarges to form the megasporocyte. In Cercis canadensis the megasporocyte is formed by direct enlargement of the archesporial cell. Meiosis occurs in all species to form a tetrad of megaspores. Frequently the micropylar dyad member in Cassia nictitans fails to undergo the second meiotic division. While only the chalazal megaspore functions in megagametogenesis, there is a tendency for the third megaspore to persist in all species. On one occasion two linear tetrads were observed in an ovule of G. triacanthos.
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