冠果草的胚胎学研究

冠果草花药壁的发育为单子口十型，绒毡层为周原质团型。小孢子母细胞减数分裂为连续型，四分体呈左右对称式排列，成熟花粉为三细胞型。双珠被，假厚珠心，倒生胚珠。胚囊发育为葱型，成熟胚囊的特点是两个极核分别位于中央细胞两端，不融合成次生核。受精过程中，一个精于与卵核融合形成合子，另一精子先与珠孔端极核融合，之后受精极核再移动到合点端与另一极核融合，形成初生胚乳核。胚的发育为石竹型。成熟胚呈马蹄形，具有2片真叶。胚乳发育为沼生目型。随着胚的发育，胚乳细胞逐渐解体，成熟种子中无胚乳。

EMBRYOLOGICAL STUDIES ON SAGITTARIA GUAYANENSIS H.B.K.SUBSP.LAPPULA (D.DON) BOJIN (ALISMATACEAE)

This paper deals with the embryological characteristics of Sagittaria guayanensis H.B.K. subsp. lappula (D.Don) Bojin. The anther wall development follows the Mono-cotyledonous type. The cytokinesis of microspore mother cell in meiosis is of the Successive type. The tetrads of microspores show an isobilateral arrangement, and the mature pollen grains are 3-celled. The ovule is bitegminous, pseudo-crassinucellate and anatropous. The megaspore mother cell originates directly from a single archesporial cell. The mature embryo sac consists of 7 cells including 8 nuclei and conforms to the Allium type. The two polar nuclei do not fuse into a secondary nucleus before fertilization. Instead, one sperm fuses with the micropylar end polar nucleus first , and the fertilized polar nucleus then migrates to the chalazal end, where it fuses with the second polar nucleus, forming the primary endosperm nucleus. The embryo development conforms to the Caryophyllad type. The mature embryo is U-shaped and forms the embryonic shoot apex accompanied by two leaves. The endosperm development corresponds to the Helobial type. The primary endosperm nucleus (invariably lying in the chalazal part of the embryo sac) divides and forms two chambers: large micropylar one and small chalazal one. The chalazal endosperm chamber remains binucleate, while, in the micropylar chamber free nuclear divisions occur and then cellularization takes place. During the embryo formation the endosperm gradually degrades and can not be found in the mature seed. The subgenus Lophotocarpus is different from the subgenus Sagittaria in some embryological aspects, especially in the structure of mature embryo sac and the double fertilization process.