Final answer:
As a magma cools, fractional crystallization causes the remaining portion of melted rock to become either fine-grained or lack crystal growth.
Step-by-step explanation:
According to Bowen's Reaction Series, as a magma cools, fractional crystallization causes the remaining portion of melted rock to become fine-grained or lack crystal growth.
This is because when magma cools quickly, there is not enough time for the individual crystals to grow large, resulting in a fine-grained texture. On the other hand, if magma cools slowly, it allows the crystals to grow larger, creating a coarse-grained texture.