Unitegmic Ovules Research Articles

Contribution to the embryology ofMelampyrum pratense L.

InMelampyrum pratense the anther is tetrasporangiate and anther wall consists of epidermis, fibrous endothecium, a transitory middle layer and glandular tapetum. The division of pollen mother cell is simultaneous. At shedding, the pollen grains are 2-celled, 3-colpate and spheroidal. The gynoecium is superior and the ovary is bicarpellary, syncarpous with two tenuinucellate, unitegmic ovules in each locule. A coenomegaspore with 1+3 arrangement of nuclei develops into a 7-nucleate embryo sac. The female gametophyte is tetrasporic and 7-nucleate. Theab initio cellular endosperm is haustorial. The chalazal haustorium is large, binucleate and highly aggressive. The 8–16 nucleate micropylar haustorium is unicellular with 2–4 tubular processes, one of which is longer and aggressive.

Floral development of Comptonia peregrina (Myricaceae)

Early stages of development of the male and female flower are similar; two second-order bracts arise in the transversal plane on either side of the floral apex before the apex flattens and becomes somewhat concave because of growth activity at the flank of the apex. In the female flower, the gynoecium develops as an extension of the girdling gynoecial primordium and the two primordial stigmas each result from more rapid growth in the median plane at the distal portion of the gynoecial wall. The floral apex resumes growth to form the unitegmic ovule. Third-order lanceolate-shaped bracts develop from a meristem situated in the axil of each second-order bract. In the male flower, staminate primordia arise at three or four loci on the ridge surrounding the apex. The apex briefly resumes growth. Growth of the second-order bracts terminates at an early stage. The floral construction is compared to other myricaceous species. It is concluded that the axillary scale-like bracts of the female flower are third-order bracts; the gynoecium does not overtop the second-order axis and the female flower is not a reduced cyme; the male flower is more floral- than inflorescence-like compared to some other myricaceous species.

DEVELOPMENT OF THE SEED AND FRUIT IN MELAMPYRUM NEMOROSUM L. AND M. ARVENSE L.

The ovary is bilocular, with four massive axile placentae, each bearing a sessile hemianatropous, unitegmic, and tenuinucellate ovule. The innermost integumentary layer forms endothelium around the micropylar part of the embryo sac. The micropylar canal is surrounded by the micropylar tube, whereas the endothelium is hypodermal in this region. The endothelium and an adjacent meristematic region contribute to the growth of the integument. The endosperm is of the Brunella type described by K. Schnarf in 1929. The chalazal haustorium is a highly aggressive, two-nucleate chamber which becomes inactive and is filled with a haustorial chalazal endosperm. The two multinucleate micropylar haustorial cells give rise to many tubular extensions which pass through the micropylar tube, but only one reaches the placenta. The cells of the storage endosperm are pitted and thickened with hemicellulose. An opaque tanniferous zone of endosperm separates the storage endosperm from the chalazal endosperm. The embryo is small and straight, with two cotyledons and a hypocotyledonary region. The seed coat is feeble, one to three layered. The pericarp is many layered and cuticularized. The two innermost lignified layers form columns at the dorsal line of the two valves of the capsule, where it dehisces. The chalazal part of the developing seed absorbs nourishment directly from the pericarp.