Megasporogenesis and Development of Female Gametophyte of Endangered Species Populus pruinosa

The megasporogenesis and development of female gametophyte of endangered species Populus pruinosa Schrenk.were studied using method of paraffin section.The results indicated that the pistil of P.pruinosa was composed of three carpels,parietal placenta,with 18 to 21 rows of anatropous ovule.At the early developmental stage,the ovule showed crassinnucellate and bitegminous,the inner integument degenerated when the outer integument developed into the same level with inner integument,the mature ovule was unitegmic.One archesporial cell differentiated from two layers beneath the epidermises.The megaspore mother cell directly developed from the archesportial cell which formed after the archesporial cell division.The megaspore mother cell undergoes meiosis to form a linear tetrad,the chalazal megaspore functions,polygonum-type embryo.During the developing of embryo,nucellus tissue of micropylar end degradated.According to the flower morphological character of flowering phenology at different growing stage,it is possible to estimate primarily the process of megasporogenesis and development of female gametophyte of P.pruinosa.