At about 10:00 EST, a Piper Archer struck trees and crashed near Haines City. The two occupants were seriously injured. The flight was en route from Crystal River, Fla., to Opa Locka and was not operating on a flight plan, although IMC prevailed along the route of flight. The pilot had received a weather briefing from the Gainesville Flight Service Station and was told VFR flight was not recommended. The pilot told line personnel at Crystal River that he would fly to the east around bad weather and then proceed south to Opa Locka.