The embryo, endosperm, and seed coat morphology in two Kenyan species of the conellaceae
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Embryological studies were made in the Kenyan trees warburgia ugandensis Sprague subsp ugandensis and warburgia stuhlmannii engl. Fertilization is porogamous. The zygote elongates considerable before undergoing division. In W Stuhlmannii, both synergids persist until the first division of the zygote, while in w ugandensis subsp ugandenssis they degenerate soon after fertilization. First division of the zygote is transverse. The embryo development conforms to the typical onagrad type. The embryonal tetrad becomes voluminous and assumes a bloobular shape. The wall of division in the middle cell of w stuhlmannii is diagonal. The lower cell of the globular tetrad enlarged, and occupies almost one half of the total volume in W Stuhlmannii. The globular stage of the proembryo has 12 cells instead of 16 cells usual for the onagrad type of embryogeny. The endosperm is ab initio cellular. Its first two divisions are transverse, forming a row of 4 superposed cells. The chalazal endosperm haustoria are present. These are one-celled uninucleate in W. stuhlamannii, and one-celled binucleate in W. ugandensis subsp. ugandensis. Rumination of the endosperm, as reported earlier for the Canellaceae, was not observed. Mature seeds are of oval shape, and medium-sized. The seed coats are formed by the integuments and remnants of the nucellus. Seed coat microsculpture in W. stuhlmannii is shallowly reticulate, while in W. ugandensis subsp. ugandensis it is deeply reticulate. This variation in the seed coat structure in the two taxa may be explained by the different dispersal mechanisms of the fruits or seeds. The embryo and endosperm are the primitive types. The results of this investigation suggest that the closest relationships of the Canellaceae should be with the Annonaceae and Chloranthaceae. These results fail to support the proposed close relationships between the Canellaceae and the Myristicaceae.