Wumu refers to five kinds of wood that were considered suitable for fire at that time. That is, "Yu; Liu Qing, so bring it in spring; Jujube: apricot red, so eat it in summer; Sang: Huang Zhe, so I took it at the end of summer; Tussah: (Mukui) white, so take autumn; Sophora japonica; Suntanned, so bring it in winter. "