1992 Volume 61 Issue 4 Pages 555-560
Auricles developing on the leaves of main stem in var. Koshihikari were the longest in the fourth leaf from the flag leaf. The length of auricle continued to become shorer than the one below and finally the auricle disappeared in the flag leaf. The author called the lowest leaf, whose auricle is shorter than the one below, "the first leaf with shortened auricle". A similar phenomenon was observed in the leaf blade, leaf ligule and leaf sheath of rice plants. Since, among these four leaf organs, the first leaf with shortened auricle appeared at the earliest developed leaf position, this was considered an important index for the optimum timing of topdressing at the ear formation stage. Its morphological changes after shooting at each leaf position were investigated. The study revealed : (1) emergence stage of the first leaf with shortened auricle was close to the initial stage of internode elongation : (2) the period from the time when the first leaf with shortened auricle was recognized to the optimum time of topdressing at the panicle formation stage (leaf number index 90∼92) was 0.60-0.90 in leaf age, four to five days in var. Nihonbare. However, this period differs from variety to variety.
