Answer: and died soon after.
Step-by-step explanation:
The plant withered and died soon after.
A dependent clause is one that cannot stand alone if not in a sentence i.e. it does not make sense as a sentence.
For example, Jane ate all the leftover because she was hungry.
In the above, the underlined is the dependent variable. Notice how it cannot be its own sentence because alone it would not make sense.
In the above, I added the dependent clause; ''and died soon after'' because it is a dependent variable as well as what usually happens to withered plants.