Chromosome doubling of female gamete in white poplars were studied in Populns tomentosa × P. balleana, P. alla × P. glandulosa and P. alba × P. tomentosa, based on megasporogenesis and megagametogenesis of cytogenetics.Now the research has made progress.(1) The meiosis stages of megaspore could be discriminated timely through observing the meiosis of microspore under the same environmental conditions, according to the association of female and male buds during development. Results indicated : The meiosis stages of megaspore of white poplars are different, while there was a association between MMCs and PMCs meiosis in the same hybrid. Megaspore mother cell just enters leptotene as The meiosis of microspore mother cell develop into tetrads . The meiosis of megaspore mother cell develop into pachytene while that of microspores develop into a single nuclear adjacent to cell wall.(2)It is practical that triploid white poplars induced by the chromosome doubling of megaspore based on the development of microspore. Under the same environmental conditions when the meiosis of microspore mother cell develop into tetrads the female buds were dipped duly with colchicine solution, which guaranteed that chromosome doubling of megaspore in white poplar could be accomplished in a short time. So much workload was cut down, and induction efficiency of triploid white poplars was also improved. 12 triploid poplars were identified among the hybrid progenies by chromosome doubling of megaspore. A high doubling efficiency of triploids (16.7%) was obtained in (P. alba × P. glandulosa) × P. tomentosa.(3) It was testified that chromosome doubling of embryo sac was the cytology mechanism of triploid induction by colchicine solution after pollination. Triploid could be obtained by the female catkins were treated with colchicine solution 24-36h after pollination in white poplar (P. alla×P. glandulosa). Asynchronism in development of embryo sac among Populus tomentosa×P. balleana, P.alla×P. glandulosa, P. alba×P. tomentosa was found by many paraffin sections observed. 48h after pollination, most them developed into eight- nuclear embryo sac after undergoing 3 times mitosis. All facts indicated that chromosome doubling of female gametes resulted from restriction of mitosis of embryo sac by colchicine solution.(4)The paper provided that the optimal receptivity of stigma was by way of the initial point for chromosome doubling of embryo sac, so which assured that a technique for chromosome doubling in embryo sac. The stigma receptive stage of white poplars(Populus tomentosa×P. balleana, P. alla×P. glandulosa, P. alba×P. tomentosa) lasted about 1 to 3 days when floral branches were cultured in water in greenhouse. The stigma of the optimal receptive stage of the three poplars were shining with a great deal secretion and opened to the flat stage -about 180°.The receptivity of the stigma was indicated by the apperance of a blue colour and air bubble with benzidine-H_2O_2 solution. In breeding, the optimal pollination stage of white poplars could be discriminated timely based on the morphological characteristics of the stigma and the changes of colour and air bubble of stigma after stained with benzidine-H_2O_2 solution.(5) The cytology mechanism of triploid induction by colchicine solution treatment after pollination was revealed. As the same time, 3 triploid white poplars were identified by chromosome doubling of embryo sac. Now many hybrid seedlings were going to be identified by chromosome counts.