[Sugi (Cryptomeria japonica D. Don) pollen scattering out of season].

We investigated the preseasonal blooming conditions of the male flowers of Sugi (Cryptomeria japonica D. Don) which flowers commonly in spring. We also investigated atmospheric Sugi pollen during all seasons for three years from 1988 through 1991 to determine pollen scattering in autumn. Our results showed that a discernible amount of pollen is scattered from the middle of October into December; this scattering would be expected in the following spring. Almost none of the buds of the flowers collected in October and in November bloomed when incubated at temperatures ranging from 6 degrees C to 20 degrees C after low-temperature treatment to arise the blooms from dormancy. However, small numbers of the male flowers from various Sugi trees bloomed and scattered pollen under these conditions. We found that the ratio of the blooming male flowers was one-third or less per blossom. The ratio changed depending on the growth stage and incubation conditions. In conclusion, the density of airborne Sugi pollen scattering is not high in autumn in general. However, the density would be expected to be high enough to induce allergic reactions and clinical symptoms in some areas of Sugi growth, especially in a good harvest year.