Ths superstition is that which ever lady catches the bouquet will be the next to marry, but I don't know where the notion comes from. It does explain why some ladies scramble to be in a catching position, and some other ladies (and men!) rush in the opposite direction.
The bride throws the bouquet because in the olden days when people were really poor, they used to have to steal the flowers from rich people's gardens. This became a well known fact and the richer classes cottoned on to where all their flowers were going, so they sneaked in to the weddings to pinch them back....then...just as they were about to take them from the bride she threw them overhead so that those unwashed little cockney kids could run away with them!.....I reckon!