Complex sentence: The first segment of the main line was completed in 1886 between Arcadia and Punta Gorda by the Florida Southern Railroad (part of Henry Plant's Plant System of railroads) as part of an extension of their line running from Lakeland and Bartow.
Split into simpler sentences: The first segment of the main line was completed in 1886 between Arcadia and Punta Gorda by the Florida Southern Railroad, which was part of Henry Plant's Plant System of railroads. It was an extension of their line running from Lakeland and Bartow.