| Summary: | 碩士 === 國立臺灣大學 === 森林學研究所 === 88 === The study was aimed to observe the phenology of shoot growth of a tree in a clonal orchard of Taiwania cryptomerioides Hay. which was set in 1966 in Chitou. We mounted the thermo-, and quantum-sensors on different aspects of crown to monitor the light intensity and temperature variation from March 22, 1999 to April 14, 2000. During this period, we also investigated morphological development, anatomic changes and mitotic index（MI）of vegetative buds of corresponding positions. The results indicated the accumulations of both heat and photosyntheically active radiation（PAR）of southern aspect of crown were higher than those of northern one, and same pattern compared upper layer with lower one of crown, but they had slight variation in different seasons. According to the comparisons of length, diameter and MI value at different aspects of crown, there were significantly different in the beginning. As time goes by, the differences of length and diameter between them become less. Furthermore, the dry weight, amount, the timing of swelling and MI of buds at different aspects of crown might also be influenced by accumulations of heat and/or PAR.
Using the MI combined with the anatomic changes to observe the growth and dormancy of vegetative buds are better than basing on morphological changes. The degree-hour model for predicting the vegetative growth was established on measured heat sums and changes of MI and anatomic changes. The estimated threshold temperature of vegetative buds was 10℃, and chilling requirement needed 65 hours. Since filling chilling requirement in the end of December 1999, to the end of March, when MI rose from zero, the average accumulation of heat was 15344 degree-hrs.
We also tried to fit the threshold temperature, chill unit and degree-hours of development of the buds from 1999-2000 to the progressive change of buds, and to establish the relations between the elongation of new shoot and degree-hours from spring 1999（April, 3）to fall 1999（September, 14）. The shoot elongation was highly related to the accumulation of heat in S-shaped curve. After 11 July, 1999, decrease of photoperiod dramatically declined the MI value and decreased the elongation rate of current shoot.
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