Genetic Variation in Seedling Development of Sitka Spruce, Picea sitchensis (Bong). Carr. 1

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Abstract
The development of the terminal bud in one-year seedlings of Sitka spruce, Picea sitchensis (Bong.) Carr., is illustrated and described as a continuous process. The same sequence of morphological events occurred in forty-seven provenances examined but the timing was different. Buds formed in response to decreasing daylength, and an essentially continuous relationship was demonstrated between time of bud formation and latitude of seed origin. Flushing was controlled largely by temperature, and time of flushing reflected the nature of the temperature régime in the native habitat. The height attained at the end of the growing season was demonstrated to be related to date of bud formation and latitude of seed origin, but the relationship was modified by temperature and photoperiod. There was little genetic variation in rate of height growth, and variability in time of bud formation was considered to be the major factor causing provenance variation in total height growth. Bud size was correlated with the number of needle primordia, but the effect of bud size on height growth was secondary, as was the effect of the number of lateral branches. The reactions of two provenances suggested that ecotypic differentiation has occurred in response to specific, local, environmental selection pressures. The results supplement the conclusions of earlier reports, namely that there is a broad interaction of genotype with environment that should be evaluated before planting the species at any given site.

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