Emerging　online　services　have　fueled　unprecedented　demands　for　multicast　transfers　across　geo-distributed　datacenters.　However,　the　time-　and　space-varying　nature　of　background　traffic　in　inter-datacenter　networks　(inter-DCNs)　makes　conventional　multicast　trees　difficult　to　fully　utilize　the　residual　bandwidth　in　the　inter-DCNs.　In　this　paper,　we　introduce　datacenter　storage　into　multicast　transfers,　and　propose　Store-and-Forward-Tree　(SnFTree)　scheduling　method　for　multicast　transfers　in　the　software-defined　optical　network.　Compared　to　the　conventional　multicast　scheduling　methods,　the　advantages　of　SnFTree　are　as　follows:　(i)　by　enabling　temporary　storage　at　intermediate　sites,　SnFTree　can　segment　the　conventional　multicast　tree　into　independent　subtrees,　which　maximizes　the　flexibility　of　provisioning;　(ii)　by　introducing　load-balancing　routing　into　the　tree　computation,　SnFTree　can　balance　the　traffic　load　across　network　efficiently;　(iii)　benefiting　from　optical　multicast,　storing,　forwarding　and　reception　can　be　simultaneously　implemented　on　a　site　with　negligible　processing　delay;　(iv)　by　formulating　the　multicast　scheduling　problem　into　a　routing　problem,　SnFTree　greatly　simplifies　the　problem　for　dynamic　traffic.　Simulations　demonstrate　that　compared　to　conventional　scheduling　methods,　SnFTree　obtains　lower　blocking　probability　and　requires　fewer　OpenFlow　Agent　Updates.