How do tree seeds fly?

Tree seeds are often found in the tree's fruits, which fall to the ground. Animals then pick up the fruits and eat them. The seeds are excreted from the animal at a later time somewhere else where they can start the growth of new trees.

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In addition, some seeds have structures that cause them to be easily blown by the wind, such as maples and cottonwoods. Those seeds will fly away on a light breeze, and start growing somewhere else.