A stalagmite differs from a stalactite in that a stalagmite

A stalagmite differs from a stalactite in that a stalagmite starts from the floor of a cave while a stalactite starts from the roof of a cave. Therefore, the correct option is "starts from the floor of a cave". Stalagmites are formed by mineral deposits that accumulate on the floor of a cave over time, usually as a result of dripping water containing dissolved minerals. On the other hand, stalactites are formed by mineral deposits that accumulate on the roof of a cave and hang downward, also as a result of dripping water containing dissolved minerals.