The study is divided into two parts. Part A is an investigation of geographic variation in immature spruce populations and refers to the growth behaviour of 150 spruce populations grown in a relatively uniform environment. The seed, which was collected throughout the white, Engelmann and Sitka spruce complex in British Columbia, was sown in a coastal nursery on Vancouver Island. Detailed measurements were made on these populations during two growing seasons. In the laboratory seed samples of the same populations were X-rayed to determine embryo development, and subsequently germinated at 25° C, Part B is a study of geographic variation in mature spruce populations and refers to a biometrical assessment of variation in cone scale morphology which was carried out on a mass collection of spruce cones collected in 157 areas throughout the range of spruce in British Columbia. This collection, therefore, embraces all four spruce species of the province. These are Sitka spruce (Picea sitchensis (Bong,) Carr.), black spruce (P. mariana (Mill,) B,S,P,), white spruce (P. glauca (Nlotnc) Voss subsp, glauca) and Engelmann spruce (P. glauca (Moench) Voss subsp, engelmannii). All measurements were subjected to statistical analysis in order to determine the relation between the variation observed and factors of the environment at place of origin. The results of both studies testify to the overwhelming influence of environmental pressures associated with altitude with respect to variation in the white-Engelmann complex. In regard to the white-Sitka complex both studies indicate the extent and effect of the penetration of Sitka spruce populations into populations of white spruce. Zones of hybridization between spruce species are characterized. The ecological significance of photoperiodic adaptation in spruce, and the relative importance of flushing and dormancy in the microevolution of the species are considered. The bearing of the results on the taxonomic status of the species in British Columbia is discussed, and recommendations are made in regard to the silviculture of the species in this province.