Abstract
Bud formation of Spiraea cantoniensis Lour.‘Mizuho’ grown at 15°, 20°, 25°C and natural temperature was investigated from the morphological point of view.
1. Spring shoots grew faster with increasing temperatures, but the shoot elongation stopped early at 20°and 25°C.
2. Number of scales of vegetative axillary bud of the spring shoot increased with increasing temperatures. Number of inner bracts (transition leaves) of the bud was approximately same in all treatments. Number of leaf primordia of the bud was the greatest at 20°C and the least at 25°C.
3. Number of leaf primordia of developed vegetative bud, except those at constant 15°C, increased few from November 1 through February 1 at constant temperatures and also under winter low temperatures.
4. At constant 15°C, inflorescences were begun to initiate five months after the start of treatment and their florets developed normally. At 20°C, inflorescences initiated two months later than those at 15°C, but all of them were abnormal ones forming bracteoles exclusively and eventually aborted at the bracteole-stage of development. No inflorescence was formed at 25°C.
5. When the plants under each temperature were transferred to outdoors on November 1 and returned to the initial temperature on February 1, most flower buds came into bloom at 15°C and 20°C, and also partially at 25°C.
