The actual effect of trichomes and protuberances on IB was examined. The number of trichomes and protuberances varied among morphological parts (Hoshikawa, 1989). Both of the abaxial and adaxial sides of leaf blades have many trichomes and protu- berances as shown in Fig 5(a). On the other hand, there are no trichomes and protuberances on the inner side of the stem. There are two areas that may or may not have many trichomes and protuberances, on the epidermis, at the outer side of the stem part. The percentage of area occupied by protuberances is about 35–50% of the outer side of the stem (Matsuda et al., 1985). As a result, there were fewer trichomes and protuberances in the stem part than in the leaf blade part. Considering that the IB of the stem part is higher than that of the leaf blade part, IB increased with decreasing the number of trichomes and protuberances.