Complex sentence: The botanist G. Ledyard Stebbins extended the synthesis to encompass botany including the important effects on speciation of hybridization and polyploidy in plants in his 1950 book "Variation and Evolution in Plants".
Split into simpler sentences: The botanist G. Ledyard Stebbins extended the synthesis to encompass botany. He described the important effects on speciation of hybridization and polyploidy in plants in his 1950 book "Variation and Evolution in Plants".