THE KINETICS OF CYTOLOGICAL EVENTS DURING DOUBLE FERTILIZATION IN ZEA-MAYS L

By using a clearing method, the process of double fertilization in Zea mays L. (line A 188) was analysed and the precise sequence of events was determined. The period from pollen tube arrival to gamete fusion w as relatively short, possibly less than 1 h. The karyogamy was of prem itotic type, and the time from the contact of male and female nuclei t o the fusion of male and female nucleoli was about 5 h in the egg cell and 3 h in the central cell. In the central cell, the sperm nucleus f used with either one of the polar nuclei or the secondary nucleus, the latter being observed for the first time in maize. The zygote was in the resting period for 13-16 h before division commenced, changing the cell polarity during karyogamy and the resting period. The primary en dosperm nucleus divided immediately after karyogamy was completed in t he central cell. The embryo sacs with two-celled proembryos contained four to eight endosperm nuclei. The timetable of fertilization events could be a standard for further studies on in vitro fertilization at t he cytological and molecular levels.