| Abstract: | The flower develops in March and blossoms in early May in Nanjing. The
cytokinesis of microsporocytes is simultaneous and most tetrads are tetrahedral. The tapetum
is secretory and the nuclei become polyploid at last. The style is solid and most ovaries are
unilocular, rarely bilocular. The ovule is pendulous, anatropous and unitegmic. The nucellus is
pseudocrassinucellate. An obturator formed by transmitting tissue covers the micropyle. The
raphe vascular strand extends into the integument when it reaches the chalaza and on a whole
keeps a “U” shape. The endothelium cell is uninucleate. In most cases no nucellar cap is
formed. No hypostase is found below the embryo sac. The archesporium is one-celled. The
embryo sac development conforms to the Polygonum or Allium types. The degeneration of
the megaspores in the linear tetrad usually occurs from the chalazal toward the micropylar
end. Two synergids persist during fertilization. Three antipodal cells are uninucleate and
ephemeral. Two polar nuclei fuse at the time of fertilization. The fertilization type accords
with porogamy. The syngamy is premitotic. The development of endosperm is cellular.
The initial four successive divisions of the primary endosperm cell are transverse-verticaltransverse-transverse subsequently, giving rise to sixteen cells of the early endosperm. The
mature embryo is straight and nearly as long as the endospermous seed. The cotyledons are
more or less cordate at base. The seedoat is thin and composed of 5-11 layers of compressed
cells. Neither embryo nor endosperm contain the alkaloid camptothecine.
The major similarities of Nyssa sinensis to the American nyssas in embryology, which
may be a counted as the generic features, are the polyploid tapetum cells, the unitegmic ovule
with U-shaped vascular strand, the direct enlargement of the archesporial cell to produce the
megasporocyte, the pseudocrassinucellus, the usual absence of the nucellar cap, the
Polygonum or Allium type of the embryo sac development, the first degeneration of the
metachalazal megaspore, the ephemeral antipodal cells, a single nucleolus in the nucleus ofthe primary endosperm cell, the more or less cordate base of the cotyledons. |
