In Paradise stand the tree of life and the tree of knowledge, the latter forming a hedge about the former. Only he who has cleared a path for himself through the tree of knowledge can come close to the tree of life, which is so huge that it would take a man five hundred years to traverse a distance equal to the diameter of the trunk, and no less vast is the space shaded by its crown of branches. From beneath it flows forth the water that irrigates the whole earth, parting thence into four streams, the Ganges, the Nile, the Tigris, and the Euphrates.
But it was only during the days of creation that the realm of plants looked to the waters of the earth for nourishment. Later on God made the plants dependent upon the rain, the upper waters. The clouds rise from earth to heaven, where water is poured into them as from a conduit. The plants began to feel the effect of the water only after Adam was created.
Although they had been brought forth on the third day, God did not permit them to sprout and appear above the surface of the earth, until Adam prayed to Him to give food unto them, for God longs for the prayers of the pious.