Maple tree produces flowers during early spring season. Around midsummer, these flowers fall and are replaced by fruit containing two seeds. These fruits, also called helicopters, contain twin seeds, each connected to a fibrous wing. As the fruits fall, they spin (and hence the name 'helicopter') and achieve a slow descent, thereby maximizing the seed dispersal area. After hitting the ground, these seed enter the soil (After the external casing dissolves) by a number of possible actions, including, soil softening by rain, animal and human activity (such as stepping on them and pushing them into the ground, etc.). Once inside the soil, these seeds will germinate within one year's time. Some seeds can remain without germination for years.
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