"It also requires synchrony in the pollen release and stigma receptivity" Din't quite understand the line. So if some one could expplain...!?
The release of pollen grains and stigma receptivity has to be synchronised means that the two things have to be in tandem or together or simultaneous or at the same time for pollen tube to form and fertilisation to occur. If pollen is released prior to the active state of the stigma in which it responds to the fallen pollen, the tube will not form and if late, then too...but if together...during the same interval of time, then everything is good to go. Hope you understood, if not, i can elaborate more.