The foundation of this world is that things are bitter at first, but sweet as well. The curse of Adam is that he has to eat vegetables. Eating the maror (bitter herb) on Pesach is the transformation of the curse into a blessing. Adam was consoled by being told that he would have to work for his food. Wheat originally grew on trees, but after the sin was it diminished to a vegetable. Trees represent a life of pleasure, while vegetables require constant toil.