Smith supports efforts to provide alternatives to embryonic stem cell research. He voted against expanding research to more embryonic stem cell lines. Wnt signaling induces blood formation from stem cells. He opposed and voted against expanding public funding of embryonic stem cell research. Treatment with stem cells is under study. There are different types of stem cells. Yamanaka focused on factors that are important for maintaining pluripotency in embryonic stem (ES) cells. The tetragametic state has important implications for organ or stem cell transplantation. Each leaf grows on its own stem. He supported limits on stem cell research. Tubers develop from either the stem or the root. This will lead to necrosis of stem and root tips and leaf edges. There are ways of improving the growth of stem cutting propagations. Castle cosponsored the Stem Cell Research Enhancement Act. Tomentose branches extend radially from a central stem.