1. In
Spiraea Thunbergii SIEB., the flower bud formation occurred in the lateral buds of current shoots.
2. The cluster differentiation stages of flower buds were observed on October 8, 1951 in Tokyo, and on October 5, 1953 in Kagawa.
3. On October 18, 1951, 10 days after the clus-ter differentiation occurred, the initial formation of pistiles was individually distinguished in Tokyo, and on October 12, 1953, 7 days after the cluster differentiation stage, the initial development of stamens was observed in Kagawa. And then the first flowers of each place began to bloom on Nov-enber 19, 1951 in Tokyo, and on November 2, 1953 in Kagawa. But they flowered little in that time, many of them flowered in middle of March in Kag-awa, and at the end of March in Tokyo.
4. In
Spiraea cantoniensis LOUR., the flower bud formation occurred in the lateral buds of current shoots.
5. The cluster differentiation stages of flower buds were observed on October 17, 1950 and on September 28, 1951 in Tokyo. And the initial for-mation of sepales, the differentiation stage of indi-vidual flower buds, occurred on Novembr 14, 1950 and on November 9, 1951.
6. The flower bud development in
Spiraea canfoniensis progressed very slowly compared with that in
S. Thunbergii; the initial formation of petals, pistiles, and pollen and ovules occurred on February 2, March 28, and April 17, 1951, in Tokyo respe-ctively. The flowers commenced to bloom on May 7.
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