甜樱桃大孢子的发生和雌配子体的形成

THE MEGASPOROGENESIS AND THE FORMATION OF FEMALE GAMETOPHYTE OF CERASUS A VIUM(L.) MOENCH

甜櫻桃单室子房内着生2个倒生胚珠,一个退化,另一个发育成种子。胚珠具单珠被,厚珠心。3月下旬大孢子母细胞形成,4月初进行减数分裂形成四分体,功能大孢子位于近合点端。花初开时,具有4～8核胚囊,开花1天后胚囊完全成熟,受精前两个极核融合为次生核。珠心帽在胚囊成熟时,具有2～7层细胞。甜樱桃的胚囊发育属蓼型。

In sweet cherry, two anatropous ovules are attached to the placenta, on the inner wall of its unilocular ovary. One of them degrades while another develops into a seed. It is a crassinucellate ovule with one integument. The megasporocyte forms in late March and undergoes meiosis to form the megaspore tetrad in early April, The functional megaspore lies nearby the chalaza end. The 4～8 nucleated embryo sac appears in early blossom and grows into mature completely at one day after flowering phase. Two polar nuclei later fuse to form the secondary nucleus before fertilization. In mature embryo sac, the nucellar cap is composed of 2～7 layer of cells. The embryo sac development of sweet cherry belongs to the Polygonum type.