The correct answer is Plessy Vs. Ferguson. In the landmark case Plessy vs. Ferguson, it was ruled that segregation of facilities was constitutional as long as those facilities were equal in quality. This is were the term "Separate but Equal" comes from. However, during the case Brown vs. The Board of Education it was ruled that racial segregation violated the fourteenth amendment of the Constitution. It was this ruling that rendered the ruling in Plessy vs. Ferguson invalid because the ruling was unconstitutional.