This is exactly why nature amazes me so much.
Willow is incredible. I made a wreath one year, and after Christmas, the kids took it for their den. When spring came, it started sprouting, even though it wasn’t in soil—just damp from the rain. 
During a storm, a big branch broke off our willow tree. I cut it into fireplace lengths and stacked it with my other firewood. A couple of weeks later, I noticed that the woodpile had branches with green leaves sprouting everywhere.
Willow has incredibly strong rooting abilities. Some people even use willow to help propagate other plants.
Willow releases so much rooting hormone into water that, in the olden days, this was the go-to method for propagating plants.
How does that really work?
Plant cells and tissues use hormones to communicate and coordinate activities like growth. One of these hormones is indolebutyric acid, which promotes root growth. Willows have a particularly high concentration of this hormone in their growing tissues. This is beneficial for them because they often live near rivers and in flood-prone areas, so a branch that breaks off can grow into a new tree downstream.
If you place willow twigs in water for a while, the water will absorb a higher concentration of this hormone. You can then put cuttings from other plants in the same water, and the hormone will stimulate root growth in them as well.
Although we can now synthesize this hormone, you can still use willow to achieve the same effect!