Abstract: Some investigations on the processes of double fertilization, endosperm development and embryogenesis, together with certain histo-chemical reactions in Ypsilandra thibetica Franch. have been made Their main features are: 1. The entry of pollen tube is porogamy and doable fertilization proceeds normally. It be longs to premitotic type. 2. The first division of the primary endosperm nucleus is followed by cell wall formation giving rise to a larger micropylar and a smaller chalazal chamber. But there is no further wall formation in the later nuclear divisions until the endosperm is nearly mature. Hence, it belongs to the Helobial type of development. Nuclear divisions tend to proceed faster in the micropylar than in the chalazal chamber and lately all freenuclei in both chambers become cellular when the proembryo consists of about four or eight cells. During the proembryogenesis some endosperm cells surrounding the proembryo degenerate gradually. 3. The zygote has a longer period of dormancy and slower rate of development than usual. When the seeds are mature, the embryos in them are not differentiated into organs yet. There are two types of embryo- genesis. Some are of the Caryophyllad type, while in others, the basal cell of the two-celled proembryo divides vertically so that two basal cells stand longitudinally parallel to each other forming the base of the suspensor. 4. The development of starch and accumulated protein grains in the process of double fertilization, embryogenesis and endosperm development were also observed.

Key words: Ypsilandra thibetica Franch., Double fertilization, Embryogenesis, Endosperm development