**2.1.5 Simplified encapsulation-vitrification**

The simplified encapsulation-vitrification method was first reported by Hirai & Sakai (2002) using shoot apices of sweet potato. The operating procedure in this method is the same as encapsulation-vitrification (see Fig. 4), however, the composition of LS differs. LS of simplified encapsulation-vitrification includes high-concentration glycerol (2.0 mol/L) and sucrose (1.6 mol/L), and the viscosity of LS is high. Although this method succeeded with sweet potato, there are some plant species which cannot be cryopreserved using high concentration glycerol (Hirai & Sakai, 1999).
