The　flowering　time　of　Arabidopsis　is　sensitive　to　climate　variability,　with　lighting　conditions　being　a　major　determinant　of　the　flowering　time.　Long-days　induce　early　flowering,　while　short-days　induce　late　flowering　or　even　no　flowers.　This　study　investigates　the　intrinsic　mechanisms　for　Arabidopsis　flowering　in　different　lighting　conditions　using　mutual　information　networks　and　logic　networks.　The　structure　parameters　of　the　mutual　information　networks　show　that　the　average　degree　and　the　average　core　clearly　distinguish　these　networks.　A　method　is　then　given　to　find　the　key　structural　genes　in　the　mutual　information　networks　and　the　logic　networks　respectively.　Ten　genes　are　found　to　possibly　promote　flowering　with　three　genes　that　may　restrain　flowering.　The　sensitivity　of　this　method　to　find　the　genes　that　promote　flowering　is　80%,　while　the　sensitivity　of　the　method　to　find　the　genes　that　restrain　flowering　is　100%　©　1996-2012　Tsinghua　University　Press.